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<pre>Network Working Group                                       L. McIntyre
Request for Comments: 2301                            Xerox Corporation
Category: Standards Track                                     S. Zilles
                                                    Adobe Systems, Inc.
                                                             R. Buckley
                                                      Xerox Corporation
                                                             D. Venable
                                                      Xerox Corporation
                                                             G. Parsons
                                                       Northern Telecom
                                                            J. Rafferty
                                                   Human Communications
                                                             March 1998



                      <span class="h1">File Format for Internet Fax</span>


Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   This document describes the TIFF (Tag Image File Format)
   representation of image data specified by the ITU-T Recommendations
   for black-and-white and color facsimile. This file format
   specification is commonly known as TIFF-FX. It formally defines
   minimal, extended and lossless JBIG modes (Profiles S, F, J) for
   black-and-white fax, and base JPEG, lossless JBIG and Mixed Raster
   Content modes (Profiles C, L, M) for color and grayscale fax. These
   modes or profiles correspond to the content of the applicable ITU-T
   Recommendations. Files formatted according to this specification use
   the image/tiff MIME Content Type.








<span class="grey">McIntyre, et. al.           Standards Track                     [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


Table of Contents

<a href="#section-1">1</a>. INTRODUCTION........................................................<a href="#page-4">4</a>
   <a href="#section-1.1">1.1</a>. Scope..........................................................<a href="#page-5">5</a>
   <a href="#section-1.2">1.2</a>. Approach.......................................................<a href="#page-5">5</a>
   <a href="#section-1.3">1.3</a>. Overview of this draft.........................................<a href="#page-5">5</a>
<a href="#section-2">2</a>. TIFF and Fax........................................................<a href="#page-7">7</a>
   <a href="#section-2.1">2.1</a>. TIFF Overview..................................................<a href="#page-7">7</a>
     <a href="#section-2.1.1">2.1.1</a>. File Structure.............................................<a href="#page-7">7</a>
     <a href="#section-2.1.2">2.1.2</a>. Image Structure............................................<a href="#page-9">9</a>
     <a href="#section-2.1.3">2.1.3</a>. TIFF File Structure for Fax Applications..................<a href="#page-10">10</a>
   <a href="#section-2.2">2.2</a> TIFF Fields for All Fax Applications...........................<a href="#page-11">11</a>
     <a href="#section-2.2.1">2.2.1</a>. TIFF Fields required for all fax modes....................<a href="#page-12">12</a>
     <a href="#section-2.2.2">2.2.2</a>. Additional TIFF Fields required for all fax modes.........<a href="#page-13">13</a>
     <a href="#section-2.2.3">2.2.3</a>. TIFF Fields recommended for all fax modes.................<a href="#page-15">15</a>
     <a href="#section-2.2.4">2.2.4</a>. New TIFF Fields recommended for fax modes.................<a href="#page-16">16</a>
<a href="#section-3">3</a>. Minimal Black-and-White Fax Mode...................................<a href="#page-18">18</a>
   <a href="#section-3.1">3.1</a>. Overview......................................................<a href="#page-18">18</a>
   <a href="#section-3.2">3.2</a>. Required TIFF Fields..........................................<a href="#page-18">18</a>
     <a href="#section-3.2.1">3.2.1</a> Baseline Fields............................................<a href="#page-18">18</a>
     <a href="#section-3.2.2">3.2.2</a> Extension Fields...........................................<a href="#page-20">20</a>
     <a href="#section-3.2.3">3.2.3</a> New Fields.................................................<a href="#page-20">20</a>
   <a href="#section-3.3">3.3</a>. Recommended TIFF Fields.......................................<a href="#page-20">20</a>
   <a href="#section-3.4">3.4</a>. End of Line (EOL) and Return to Control (RTC).................<a href="#page-20">20</a>
     <a href="#section-3.4.1">3.4.1</a> RTC Exclusion..............................................<a href="#page-21">21</a>
   <a href="#section-3.5">3.5</a>. File Structure................................................<a href="#page-22">22</a>
   <a href="#section-3.6">3.6</a>. Minimal Black-and-White Mode Summary..........................<a href="#page-23">23</a>
<a href="#section-4">4</a>. Extended Black-and-White Fax Mode..................................<a href="#page-24">24</a>
   <a href="#section-4.1">4.1</a>. TIFF-F Overview...............................................<a href="#page-25">25</a>
   <a href="#section-4.2">4.2</a>. Required TIFF Fields..........................................<a href="#page-26">26</a>
     <a href="#section-4.2.1">4.2.1</a>. Baseline Fields...........................................<a href="#page-26">26</a>
     <a href="#section-4.2.2">4.2.2</a>. Extension Fields..........................................<a href="#page-28">28</a>
     <a href="#section-4.2.3">4.2.3</a>. New Fields................................................<a href="#page-29">29</a>
   <a href="#section-4.3">4.3</a>. Recommended TIFF Fields.......................................<a href="#page-29">29</a>
     <a href="#section-4.3.1">4.3.1</a>. Baseline Fields...........................................<a href="#page-29">29</a>
     <a href="#section-4.3.2">4.3.2</a>. Extension Fields..........................................<a href="#page-29">29</a>
     <a href="#section-4.3.3">4.3.3</a>. New Fields................................................<a href="#page-29">29</a>
   <a href="#section-4.4">4.4</a>. Technical Implementation Issues...............................<a href="#page-30">30</a>
     <a href="#section-4.4.1">4.4.1</a>. Strips....................................................<a href="#page-30">30</a>
     <a href="#section-4.4.2">4.4.2</a>. Bit Order.................................................<a href="#page-31">31</a>
     <a href="#section-4.4.3">4.4.3</a>. Multi-Page................................................<a href="#page-31">31</a>
     <a href="#section-4.4.4">4.4.4</a>. Compression...............................................<a href="#page-31">31</a>
     <a href="#section-4.4.5">4.4.5</a>. Example Use of Page-quality Fields........................<a href="#page-32">32</a>
     4.4.6. Practical Guidelines for Writing and Reading Multi-Page
            TIFF-F Files..............................................<a href="#page-33">33</a>
     <a href="#section-4.4.7">4.4.7</a>. Use of TIFF-F for Streaming Applications..................<a href="#page-34">34</a>
   <a href="#section-4.5">4.5</a>. Implementation Warnings.......................................<a href="#page-34">34</a>
     <a href="#section-4.5.1">4.5.1</a>. Uncompressed Data.........................................<a href="#page-34">34</a>



<span class="grey">McIntyre, et. al.           Standards Track                     [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


     <a href="#section-4.5.2">4.5.2</a>. Encoding and Resolution...................................<a href="#page-35">35</a>
     <a href="#section-4.5.3">4.5.3</a>. EOL byte-aligned..........................................<a href="#page-35">35</a>
     <a href="#section-4.5.4">4.5.4</a>. EOL.......................................................<a href="#page-36">36</a>
     <a href="#section-4.5.5">4.5.5</a>. RTC Exclusion.............................................<a href="#page-36">36</a>
     <a href="#section-4.5.6">4.5.6</a>. Use of EOFB for T.6 Compressed Images.....................<a href="#page-37">37</a>
   <a href="#section-4.6">4.6</a>. Example Use of TIFF-F.........................................<a href="#page-37">37</a>
   <a href="#section-4.7">4.7</a>. Extended Black-and-white Fax Mode Summary.....................<a href="#page-37">37</a>
<a href="#section-5">5</a>. Lossless JBIG Black-and-White Fax Mode.............................<a href="#page-39">39</a>
   <a href="#section-5.1">5.1</a>. Overview......................................................<a href="#page-40">40</a>
   <a href="#section-5.2">5.2</a>. Required TIFF Fields..........................................<a href="#page-40">40</a>
     <a href="#section-5.2.1">5.2.1</a>. Baseline Fields...........................................<a href="#page-40">40</a>
     <a href="#section-5.2.2">5.2.2</a>. Extension Fields..........................................<a href="#page-40">40</a>
     <a href="#section-5.2.3">5.2.3</a>. New Fields................................................<a href="#page-41">41</a>
   <a href="#section-5.3">5.3</a>. Recommended TIFF Fields.......................................<a href="#page-41">41</a>
   <a href="#section-5.4">5.4</a>. Lossless JBIG Black-and-White Mode Summary....................<a href="#page-41">41</a>
<a href="#section-6">6</a>. Base Color Fax Mode................................................<a href="#page-43">43</a>
   <a href="#section-6.1">6.1</a>. Overview......................................................<a href="#page-43">43</a>
   <a href="#section-6.2">6.2</a>. Required TIFF Fields..........................................<a href="#page-43">43</a>
     <a href="#section-6.2.1">6.2.1</a>. Baseline Fields...........................................<a href="#page-43">43</a>
     <a href="#section-6.2.2">6.2.2</a>. Extension Fields..........................................<a href="#page-45">45</a>
     <a href="#section-6.2.3">6.2.3</a>. New Fields................................................<a href="#page-46">46</a>
   <a href="#section-6.3">6.3</a>. Recommended TIFF Fields.......................................<a href="#page-47">47</a>
   <a href="#section-6.4">6.4</a>. Base Color Fax Mode Summary...................................<a href="#page-47">47</a>
<a href="#section-7">7</a>. Lossless Color Mode................................................<a href="#page-49">49</a>
   <a href="#section-7.1">7.1</a>. Overview......................................................<a href="#page-50">50</a>
     <a href="#section-7.1.1">7.1.1</a>. Color Encoding............................................<a href="#page-50">50</a>
     <a href="#section-7.1.2">7.1.2</a>. JBIG Encoding.............................................<a href="#page-50">50</a>
   <a href="#section-7.2">7.2</a>. Required TIFF Fields..........................................<a href="#page-51">51</a>
     <a href="#section-7.2.1">7.2.1</a>. Baseline Fields...........................................<a href="#page-51">51</a>
     <a href="#section-7.2.2">7.2.2</a>. Extension Fields..........................................<a href="#page-52">52</a>
     <a href="#section-7.2.3">7.2.3</a>. New Fields................................................<a href="#page-53">53</a>
   <a href="#section-7.3">7.3</a>. Recommended TIFF Fields.......................................<a href="#page-53">53</a>
   <a href="#section-7.4">7.4</a>. Lossless Color Fax Mode Summary...............................<a href="#page-53">53</a>
<a href="#section-8">8</a>. Mixed Raster Content Mode..........................................<a href="#page-55">55</a>
   <a href="#section-8.1">8.1</a> Overview.......................................................<a href="#page-55">55</a>
     <a href="#section-8.1.1">8.1.1</a>. MRC 3-layer model.........................................<a href="#page-55">55</a>
     <a href="#section-8.1.2">8.1.2</a>. A TIFF Representation for the MRC 3-layer model...........<a href="#page-56">56</a>
   <a href="#section-8.2">8.2</a>. Required TIFF Fields..........................................<a href="#page-58">58</a>
     <a href="#section-8.2.1">8.2.1</a>. Baseline Fields...........................................<a href="#page-58">58</a>
     <a href="#section-8.2.2">8.2.2</a>. Extension Fields..........................................<a href="#page-59">59</a>
     <a href="#section-8.2.3">8.2.3</a>. New Fields................................................<a href="#page-60">60</a>
   <a href="#section-8.3">8.3</a>. Recommended TIFF Fields.......................................<a href="#page-62">62</a>
   <a href="#section-8.4">8.4</a>. Rules and Requirements for Images.............................<a href="#page-62">62</a>
   <a href="#section-8.5">8.5</a>. MRC Fax Mode Summary..........................................<a href="#page-63">63</a>
<a href="#section-9">9</a>. MIME content-type image/tiff.......................................<a href="#page-66">66</a>
   9.1 Refinement of MIME content-type image/tiff for Facsimile
       Applications...................................................<a href="#page-66">66</a>
<a href="#section-10">10</a>. Security Considerations...........................................<a href="#page-67">67</a>



<span class="grey">McIntyre, et. al.           Standards Track                     [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


<a href="#section-11">11</a>. References........................................................<a href="#page-67">67</a>
<a href="#section-12">12</a>. Authors' Addresses................................................<a href="#page-69">69</a>
Annex A: Summary of TIFF Fields for Internet Fax .....................<a href="#page-70">70</a>
Annex B. IANA Registration for image/tiff Application Parameter
         Values used for facsimile....................................<a href="#page-75">75</a>
Full Copyright Statement..............................................<a href="#page-77">77</a>

<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>

   This document describes the use of TIFF (Tag Image File Format) to
   represent the data content and structure generated by the current
   suite of ITU-T Recommendations for Group 3 facsimile. These
   Recommendations and the TIFF fields described here support the
   following facsimile modes or profiles:

      S:  minimal black-and-white mode, using binary MH compression
             [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>]
      F:  extended black-and-white mode, using binary MH, MR and MMR
             compression [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>, <a href="#ref-T.6" title="Facsimile coding schemes and coding control functions for group 4 facsimile apparatus">T.6</a>]
      J:  lossless JBIG black-and-white mode, with JBIG compression
             [<a href="#ref-T.85" title="Application profile for Recommendation T.82 - Progressive bi-level image compression (JBIG coding scheme) for facsimile apparatus">T.85</a>, <a href="#ref-T.82" title="Information technology - Coded representation of picture and audio information - Progressive bi- level image compression">T.82</a>]
      C:  lossy color and grayscale mode, using JPEG compression
             [<a href="#ref-T.42" title="Continuous-tone colour representation method for facsimile">T.42</a>, <a href="#ref-T.81" title="Information technology - Digital compression and coding of continuous-tone still images - Requirements and guidelines">T.81</a>]
      L:  lossless color and grayscale mode, using JBIG compression
             [<a href="#ref-T.43" title="Colour and gray-scale image representations using lossless coding scheme for facsimile">T.43</a>, <a href="#ref-T.82" title="Information technology - Coded representation of picture and audio information - Progressive bi- level image compression">T.82</a>]
      M:  mixed raster content mode [<a href="#ref-T.44" title="Mixed Raster Content (MRC)">T.44</a>], using a combination of
             existing compression methods

   Each profile corresponds to the content of ITU-T Recommendations
   shown and is a subset of the full TIFF for facsimile specification.

   Profile S describes a minimal interchange set of fields, which will
   guarantee that, at least, binary black-and-white images will be
   supported. Implementations are required to support this minimal
   interchange set of fields.

   With the intent of specifying a file format for Internet Fax, this
   draft:

       1.  specifies the structure of TIFF files for facsimile data,
       2.  defines ITU fax-compatible values for existing TIFF fields,
       3.  defines new TIFF fields and values required for compatibility
           with ITU color fax.

   This specification of TIFF for facsimile is known as TIFF-FX.






<span class="grey">McIntyre, et. al.           Standards Track                     [Page 4]</span></pre>
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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a> Scope</span>

   This document defines a TIFF-based file format specification for
   enabling standardized messaging-based fax over the Internet. It
   specifies the TIFF fields and field values required for compatibility
   with the existing ITU-T Recommendations for Group 3 black-and-white,
   grayscale and color facsimile. TIFF has historically been used for
   handling fax image files in applications such as store-and-forward
   messaging.  Implementations that support this file format
   specification for import/export may elect to support it as a native
   format. This document recommends a TIFF file structure that is
   compatible with low-memory and page-level streaming implementations.

   Unless otherwise noted, the current TIFF specification [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] and
   selected TIFF Technical Notes [<a href="#ref-TTN1" title="1995">TTN1</a>, <a href="#ref-TTN2" title="1995">TTN2</a>] are the primary references
   for describing TIFF and defining TIFF fields. This document is the
   primary reference for defining TIFF field values for fax
   applications.

<span class="h3"><a class="selflink" id="section-1.2" href="#section-1.2">1.2</a> Approach</span>

   The basic approach to using TIFF for facsimile data is to insert the
   compressed fax image data in a TIFF file and use TIFF fields to
   encode the parameters that describe the image data. These fields will
   have values that comply with the ITU-T Recommendations. The MIME
   content type of the resulting file will be image/tiff, with an
   optional Application parameter [<a href="#ref-TIFF-REG" title="&quot;Tag Image File Format (TIFF) - image/tiff MIME Sub-type Registration&quot;">TIFF-REG</a>]; see <a href="#section-9">Section 9</a>.

   This approach takes advantage of TIFF features and structures that
   bridge the data formats and performance requirements of both legacy
   fax machines and host-based fax applications. TIFF constructs for
   pages, images, and strips allow a TIFF file to preserve the fax data
   stream structure and the performance advantages that come with it. A
   TIFF-based approach also builds on an established base of users and
   implementors and ensures backward compatibility with existing TIFF-
   based IETF proposals and work in progress for Internet fax.

<span class="h3"><a class="selflink" id="section-1.3" href="#section-1.3">1.3</a> Overview of this draft</span>

   <a href="#section-2">Section 2</a> gives an overview of TIFF. <a href="#section-2.1">Section 2.1</a> describes the
   structure of TIFF files, including general guidelines for structuring
   multi-page TIFF files. <a href="#section-2.2">Section 2.2</a> lists the TIFF fields that are
   required or recommended for all fax modes. The TIFF fields used only
   by specific fax modes are described in Sections <a href="#section-3">3</a>-<a href="#section-8">8</a>, which describe
   the individual fax modes. These sections also specify the ITU-
   compatible field values (image parameters) for each mode.





<span class="grey">McIntyre, et. al.           Standards Track                     [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   The full set of permitted fields of TIFF for facsimile are included
   in the current TIFF specification, <a href="#section-2">Section 2</a> of this document and the
   sections on specific modes of facsimile operation. This document
   defines profiles of TIFF for facsimile, where a profile is a subset
   of the full set of permitted fields and field values of TIFF for
   facsimile.

   <a href="#section-3">Section 3</a> defines the minimal black-and-white facsimile mode (Profile
   S), which is required in all implementations. <a href="#section-4">Section 4</a> defines the
   extended black-and-white fax mode (Profile F), which provides a
   standard definition of TIFF-F. <a href="#section-5">Section 5</a> describes the lossless
   black-and-white mode using JBIG compression (Profile J). <a href="#section-6">Section 6</a>
   defines the base color mode, required in all color implementations,
   for the lossy JPEG representation of color and grayscale facsimile
   data (Profile C). <a href="#section-7">Section 7</a> defines the lossless JBIG color and
   grayscale facsimile mode (Profile L) and <a href="#section-8">Section 8</a> defines the Mixed
   Raster Content facsimile mode (Profile M). Each of these sections
   concludes with a table summarizing the required and recommended
   fields for each mode and the values they can have.

   <a href="#section-9">Section 9</a> describes the MIME content type image/tiff and the use of
   the optional Application parameter in connection with TIFF for
   facsimile. Sections <a href="#section-10">10</a>, <a href="#section-11">11</a>, <a href="#section-12">12</a> and <a href="#section-13">13</a> give Security Considerations,
   the ISOC Copyright Notice, References and Authors' Addresses. Annex A
   gives a summary of the TIFF fields used or defined in this document
   and provides a convenient reference for implementors.

   To implement only the minimal interchange black-and-white set of
   fields and values (Profile S), one need read only Sections <a href="#section-1">1</a>, <a href="#section-2">2</a>, <a href="#section-3">3</a>, <a href="#section-9">9</a>
   and 10.

   The following tree diagram shows the relationship among profiles and
   between profiles and coding methods.

                                S (MH)
                               / \
                       B&amp;W    /   \   Color
                  ------------     ----------
                 /      \                    \
                /        F (MMR, MR)          C (JPEG)
               /                             / \
              J (JBIG)                   ----   \
                                        /        \
                                       L (JBIG)   \
                                                   \
                                                    M (MRC)

   A profile is based on a collection of ITU-T facsimile coding methods.



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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   For example, Profile S, the minimal mode, is based on Modified
   Huffman (MH) compression, which are defined in ITU-T Rec. T.4.
   Profile F specifies Modified Read (MR) and Modified Modified Read
   (MMR) compressions, which are defined in ITU-T Rec. T.4 and T.6.

   All implementations of TIFF for facsimile MUST implement Profile S,
   which is the root node of the tree. All color implementations of TIFF
   for facsimile MUST implement Profile C. The implementation of a
   particular profile MUST also implement those profiles on the path
   that connect it to the root node, and MAY optionally implement
   profiles not on the path connecting it to the root node. For example,
   an implementation of Profile M must also implement Profiles C and S,
   and may optionally implement Profile F, J or L. For another example,
   an implementation of Profile C must also implement Profile S, and may
   optionally implement Profile F or J.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", " NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [<a href="#ref-REQ" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">REQ</a>].

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. TIFF and Fax</span>

<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>. TIFF Overview</span>

   TIFF provides a means for describing, storing and interchanging
   raster image data. A primary goal of TIFF is to provide a rich
   environment within which applications can exchange image data. The
   current TIFF specification [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] defines a commonly used, core set
   of TIFF fields known as Baseline TIFF. The current specification and
   TIFF Technical Notes 1 and 2 [<a href="#ref-TTN1" title="1995">TTN1</a>, <a href="#ref-TTN2" title="1995">TTN2</a>] define several TIFF
   extensions. The TIFF- based specification for fax applications uses a
   subset of Baseline TIFF fields, with selected extensions, as
   described in this document. In a few cases, this document defines new
   TIFF fields specifically for fax applications.

<span class="h4"><a class="selflink" id="section-2.1.1" href="#section-2.1.1">2.1.1</a>. File Structure</span>

   TIFF is designed for raster images, which makes it a good match for
   facsimile documents, which are multi-page raster images. Each raster
   image consists of a number of rows or scanlines, each of which has
   the same number of pixels, the unit of sampling. Each pixel has at
   least one sample or component (exactly one for black-and-white
   images).

   A TIFF file begins with an 8-byte image file header. The first two
   bytes describe the byte order used within the file. Legal values are
   "II" (0x4949) when bytes are ordered from least to most significant
   (little- endian), and "MM" (0x4D4D), when bytes are ordered from most



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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   to least significant (big-endian) within a 16- or 32-bit integer.
   Either byte order can be used, except in the case of the minimal
   black-and-white mode, which SHALL use value "II". The next two bytes
   contain the value 42 that identifies the file as a TIFF file and is
   ordered according to the value in the first two bytes of the header.
   The last four bytes give the offset that points to the first image
   file directory (IFD). This and all other offsets in a TIFF file are
   with respect to the beginning of the TIFF file. An IFD can be at any
   location in the file after the header but must begin on a word
   boundary.

   An IFD is a sequence of tagged fields, sorted in ascending order by
   tag value. An IFD consists of a 2-byte count of the number of fields,
   a sequence of field entries and a 4-byte offset to the next IFD. The
   fields contain information about the image and pointers to the image
   data. Each separate raster image in the file is represented by an
   IFD.

   Each field entry in an IFD has 12 bytes and consists of a 2-byte Tag,
   2 bytes identifying the field type (e.g. short, long, rational,
   ASCII), 4 bytes giving the count (number of values or offsets), and 4
   bytes that either contain the offset to a field value stored outside
   the IFD, or, based on the type and count, the field value itself.
   Resolution and metadata such as dates, names and descriptions are
   examples of "long" field values that do not fit in 4 bytes and
   therefore use offsets in the field entry. Details are given in the
   TIFF specification [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>].

   A TIFF file can contain more than one IFD, where each IFD is a
   subfile whose type is given in the NewSubfileType field. Multiple
   IFDs can be organized either as a linked list, with the last entry in
   each IFD pointing to the next IFD (the pointer in the last IFD is 0),
   or as a tree, using the SubIFDs field in the primary IFD [<a href="#ref-TTN1" title="1995">TTN1</a>]. The
   SubIFDs field contains an array of pointers to child IFDs of the
   primary IFD.

   Child IFDs describe related images, such as reduced resolution
   versions of the primary IFD image. The same IFD can point both to a
   next IFD and to child IFDs, and child IFDs can themselves point to
   other IFDs.

   All fax modes represent a multi-page fax image as a linked list of
   IFDs, with a NewSubfileType field containing a bit that identifies
   the IFD as one page of a multi-page document. Each IFD has a
   PageNumber field, identifying the page number in ascending order,
   starting at 0 for the first page. While a Baseline TIFF reader is not





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   required to read any IFDs beyond the first, an implementation that
   reads the files that comply with this specification SHALL read
   multiple IFDs. Only the Mixed Raster Content fax mode, described in
   <a href="#section-8">Section 8</a>, requires the use of child IFDs.

   The following figure illustrates the structure of a multi-page TIFF
   file.

                   +-----------------------+
                   |         Header        |------------+
                   +-----------------------+            | First IFD
                   |      IFD (page 0)     |&lt;-----------+ Offset
               +---|                       |------------+
         Value |   +-----------------------+            |
        Offset +--&gt;|      Long Values      |--+         |
                   +-----------------------|  | Strip   |
                   |       Image Data      |&lt;-+ Offset  |
                   |     strip 1 page 0    |  |         |
                   +-----------------------+  |         |
                   |           :           |  :         |
                                                        |
                   +-----------------------+            | Next IFD
                   |      IFD (page 1)     |&lt;-----------+ Offset
               +---|                       |------------+
         Value |   +-----------------------+            |
        Offset +--&gt;|      Long Values      |--+         |
                   +-----------------------|  | Strip   |
                   |       Image Data      |&lt;-+ Offset  |
                   |     strip 1 page 1    |  |         |
                   +-----------------------+  |         |
                   |     strip 2 page 1    |&lt;-+         |
                   +-----------------------+  |         |
                   |          :            |  :         |
                                                        |
                   +-----------------------+            | Next IFD
                   |      IFD (page 2)     |&lt;-----------+ Offset
                   |          :            |

<span class="h4"><a class="selflink" id="section-2.1.2" href="#section-2.1.2">2.1.2</a> Image Structure</span>

   An IFD stores an image as one or more strips, as shown in the
   preceding figure. A strip consists of 1 or more scanlines (rows) of
   raster image data in compressed form. An image may be stored in a
   single strip or may be divided into several strips, which would
   require less memory to buffer. (Baseline TIFF recommends about 8k
   bytes per strip, but existing fax usage is typically one strip per
   image.)




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   Each IFD requires three strip-related fields: StripOffsets,
   RowsPerStrip and StripByteCounts. The StripOffsets field is an array
   of pointers to the strip or strips that contain the actual image
   data. The StripByteCounts field gives the number of bytes in each
   strip after compression. TIFF requires that each strip, except the
   last, contain the same number of scanlines, which is given in the
   RowsPerStrip field. This document introduces the new StripRowCounts
   field that allows a variable number of scanlines per strip, which is
   required by the Mixed Raster Content fax mode (<a href="#section-8">Section 8</a>).

   Image data is stored as uninterpreted, compressed image data streams
   within a strip. The formats of these streams follow the ITU-T
   Recommendations. The Compression field in the IFD indicates the type
   of compression, and other TIFF fields in the IFD describe image
   attributes, such as color encoding and spatial resolution.
   Compression parameters are stored in the compressed data stream,
   rather than in TIFF fields. This makes the TIFF representation and
   compressed data format specification independent of each another.
   This approach, modeled on [<a href="#ref-TTN2" title="1995">TTN2</a>], allows TIFF to gracefully add new
   compression schemes as they become available.

   Some attributes can be specified both in the compressed data stream
   and within a TIFF field. It is possible that the two values will
   differ. When this happens for values required to interpret the data
   stream, then the values in the data stream take precedence. For
   informational values that are not required to interpret the data
   stream, such as author name, then the TIFF field value takes
   precedence.

<span class="h4"><a class="selflink" id="section-2.1.3" href="#section-2.1.3">2.1.3</a> TIFF File Structure for Fax Applications</span>

   The TIFF specification has a very flexible file structure, which does
   not specify the ordering of IFDs, field values and image data in a
   file. Individual applications may require or recommend an ordering.

   This specification recommends that when using a TIFF file for
   facsimile, A multi-page fax document SHOULD be represented as a
   linked list of IFDs. It also recommends that a TIFF file for
   facsimile SHOULD order pages in a TIFF file in the same way that they
   are ordered in a fax data stream. In a TIFF file, a page consists of
   several elements: one or more IFDs (including subIFDs), long field
   values that are stored outside the IFDs, and image data (in one or
   more strips).

   The minimal black-and-white mode (Profile S) specifies a required
   ordering of pages and elements within a page (<a href="#section-3.5">Section 3.5</a>). The
   extended black-and-white mode (Profile F) provides guidelines for
   ordering pages and page elements (<a href="#section-4.4.6">Section 4.4.6</a>). Other profiles



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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   SHOULD follow these guidelines. This recommendation is intended to
   simplify the implementation of TIFF writers and readers in fax
   applications and the conversion between TIFF file and fax data stream
   representations. However, for interchange robustness, readers SHOULD
   be prepared to read TIFF files whose structure is consistent with
   [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>], which supports a more flexible file structure than is
   recommended here.

   This specification introduces an optional new GlobalParametersIFD
   field, defined in <a href="#section-2.2.4">Section 2.2.4</a>. This field has type IFD and
   indicates parameters describing the fax session. While it is often
   possible to obtain these parameters by scanning the file, it is
   convenient to make them available together in one place for fast and
   easy access. If the GlobalParametersIFD occurs in a TIFF file, it
   SHOULD be located in the first IFD, immediately following the 8-byte
   image file header.

<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a> TIFF Fields for All Fax Applications</span>

   The TIFF specification [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] is organized as a baseline set and
   several extensions, including technical notes [<a href="#ref-TTN1" title="1995">TTN1</a>, <a href="#ref-TTN2" title="1995">TTN2</a>] that will
   be incorporated in the next release of TIFF. The baseline and
   extensions have required and optional fields.

   Facsimile applications require (and recommend) a mixture of baseline
   and extensions fields, as well as some new fields that are not part
   of the TIFF specification and that are defined in this document. This
   sub- section lists the fields that are required or recommended for
   all modes. In particular, <a href="#section-2.2.1">Section 2.2.1</a> lists the fields that are
   required by all modes and that have values that do not depend on the
   mode. <a href="#section-2.2.2">Section 2.2.2</a> lists the fields that are required by all modes
   and that have values which do depend on the mode. <a href="#section-2.2.3">Section 2.2.3</a> lists
   the fields that are recommended for all modes. Fields that are
   required or recommended by some but not all modes are given in the
   section (<a href="#section-3">Section 3</a>-8) that describes that mode. The sections for each
   fax mode have sub-sections for required and recommended fields; each
   sub-section organizes the fields according to whether they are
   baseline, extension or new.

   The fields required for facsimile have only a few legal values,
   specified in the ITU-T Recommendations. Of these legal values, some
   are required and some are optional, just as they are required
   (mandatory) or optional in fax implementations that conform to the
   ITU-T Recommendations. The required and optional values are noted in
   the sections on the different fax modes.






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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   This section describes the fields required or recommended by all fax
   modes. The pattern for the description of TIFF fields in this draft
   is:

FieldName(TagValueInDecimal) = allowable values.                    TYPE
    WhetherRequiredByTIFForTIFFforFAX
    Count = (omitted if =1) = (if not in current spec but available)
    Explanation of the field, how it's used, and the values it can have.
    Default value, if any, as specified in [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>]

   When a field's default value is the desired value, that field may be
   omitted from the relevant IFD unless specifically required by the
   text of this specification.

<span class="h4"><a class="selflink" id="section-2.2.1" href="#section-2.2.1">2.2.1</a>.  TIFF fields required for all fax modes</span>

   The TIFF fields listed in this section SHALL be used by all fax
   modes, but have field values that are not specified by the ITU
   standards, i.e. the fields do not depend on the mode. The next sub-
   section lists the fields that SHALL be used by all fax modes, but
   which do have values specified by the ITU-specified or mode-specific
   values. Fields that SHALL be used by some but not all modes are given
   in the sections (3-8) which describe the modes that uses them.

ImageLength(257)                                           SHORT or LONG
    RequiredByTIFFBaseline
    Total number of scanlines in image.
    No default, must be specified.

PageNumber(297)                                                    SHORT
    RequiredByTIFFforFAX, TIFFExtension
    Count = 2
    The first number represents the page number (0 for the first page);
    the second number is the total number of pages in the document. If
    the second value is 0, then the total page count is not available.
    No default, must be specified

RowsPerStrip(278)                                          SHORT or LONG
    RequiredByTIFFBaseline
    The number of scanlines per TIFF strip, except for the last strip.
    For a single strip image, this is the same as the value of the
    ImageLength field.
    Default = 2**32 - 1 (meaning all scanlines in one strip)

StripByteCounts(279)                                       SHORT or LONG
    RequiredByTIFFBaseline
    Count = number of strips
    For each strip, the number of bytes in that strip after compression.



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    No default, must be specified.

StripOffsets(273)                                          SHORT or LONG
    RequiredByTIFFBaseline
    Count = number of strips
    For each strip, the byte offset from the beginning of the file to
    the start of that strip.
    No default, must be specified.

<span class="h4"><a class="selflink" id="section-2.2.2" href="#section-2.2.2">2.2.2</a> Additional TIFF fields required for all fax modes</span>

   The TIFF fields listed in this section SHALL be used by all fax
   modes, but the values associated with them depend on the mode being
   described and the associated ITU Recommendations. Therefore, only the
   fields are defined here; the values applicable to a particular fax
   mode are described in Sections <a href="#section-3">3</a>-<a href="#section-8">8</a>. Fields that SHALL be used by some
   but not all modes are given in the section (3-8) describing the mode
   that uses them.

BitsPerSample(258)                                                 SHORT
    RequiredByTIFFBaseline
    Number of bits per image sample
    Default = 1 (field may be omitted if this is the value)

Compression(259)                                                   SHORT
    RequiredByTIFFBaseline
    Compression method used for image data
    Default = 1 (no compression, so may not be omitted for FAX)

FillOrder(266)                                                     SHORT
    RequiredByTIFFforFax
    The default bit order in Baseline TIFF per [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] is indicated by
    FillOrder=1, where bits are not reversed before being stored.
    However, TIFF for Fax typically utilizes the setting of FillOrder=2,
    where the bit order within bytes is reversed before storage (i.e.,
    bits are stored with the Least Significant Bit first).
    Default = 1 (field may be omitted if this is the value)
    Facsimile data appears on the phone line in bit-reversed order
    relative to its description in the relevant ITU compression
    Recommendation. Therefore, a wide majority of facsimile
    implementations choose this natural order for storage. Nevertheless,
    all readers conforming to this specification must be able to read
    data in both bit orders.

ImageWidth(256)                                            SHORT or LONG
    RequiredByTIFFBaseline
    The number of pixels (columns) per scanline (row) of the image
    No default, must be specified.



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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


NewSubFileType(254)                                                 LONG
    RequiredByTIFFforFAX
    A general indication of the kind of data contained in this IFD
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for FAX)

PhotometricInterpretation(262)                                     SHORT
    RequiredByTIFFBaseline
    The color space of the image data
    No default, must be specified

ResolutionUnit(296)                                                SHORT
    RequiredByTIFFBaseline
    The unit of measure for resolution. 2 = inch, 3 = centimeter;
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277)                                               SHORT
    RequiredByTIFFBaseline
    The number of color components per pixel; SamplesPerPixel is 1 for a
    black-and-white, grayscale or indexed (palette) image.
    Default =1 (field may be omitted if this is the value)

XResolution(282)                                                RATIONAL
    RequiredByTIFFBaseline
    The horizontal resolution of the image in pixels per resolution
    unit. The ITU-T Recommendations for facsimile specify a small number
    of horizontal resolutions: 100, 200, 300, 400 pixels per inch, and
    80, 160 pixels per centimeter (or 204, 408 pixels per inch). The
    allowed XResolution values for each mode are given in the section
    defining that mode. Per [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>], it is permissible for applications to
    treat the following XResolution values as being equivalent: &lt;204,
    200&gt; and &lt;400,408&gt; in pixels/inch. These equivalencies were allowed
    by [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>] to permit conversions between inch and metric based
    facsimile terminals.
    TIFF for Facsimile Writers SHOULD express XResolution in inch based
    units, for consistency with historical practice and to maximize
    interoperability. See the table below for information on how to
    convert from an ITU-T metric value to its inch based equivalent
    resolution.
    No default, must be specified

YResolution(283)                                                RATIONAL
    RequiredByTIFFBaseline
    The vertical resolution of the image in pixels per resolution unit.
    The ITU-T Recommendations for facsimile specify a small number of
    vertical resolutions: 100, 200, 300, 400 pixels per inch, and 38.5,
    77, 154 pixels per centimeter (or 98, 196, 391 pixels per inch). The
    allowed YResolution values for each mode are given in the section



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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


    defining that mode. Per [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>], it is permissible for applications to
    treat the following YResolution values as being equivalent: &lt;98,
    100&gt;, &lt;196, 200&gt;, and &lt;391, 400&gt; in pixels/inch. These equivalencies
    were allowed by [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>] to permit conversions between inch and metric
    based facsimile terminals. TIFF for Facsimile Writers SHOULD express
    YResolution in inch based units, for consistency with historical
    practice and to maximize interoperability. See the table below for
    information on how to convert from an ITU-T metric value to its inch
    based equivalent resolution. No default, must be specified

      +-----------------------------+-----------------------------+
      |         XResolution         |         YResolution         |
      +--------------+--------------+--------------+--------------+
      |ResolutionUnit|ResolutionUnit|ResolutionUnit|ResolutionUnit|
      |  =2 (inch)   |   =3 (cm)    |  =2 (inch)   |   =3 (cm)    |
      +--------------+--------------+--------------+--------------+
      |     100      |              |     100      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |      98      |     38.5     |
      |     200      |              |     100      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |     196      |      77      |
      |     200      |              |     200      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |     391      |     154      |
      +--------------+--------------+--------------+--------------+
      |     300      |              |     300      |              |
      +--------------+--------------+--------------+--------------+
      |     408      |     160      |     391      |     154      |
      |     400      |              |     400      |              |
      +--------------+--------------+--------------+--------------+

<span class="h4"><a class="selflink" id="section-2.2.3" href="#section-2.2.3">2.2.3</a> TIFF fields recommended for all fax modes</span>

   The TIFF fields listed in this section MAY be used by all fax modes.
   However, Profile S writers (the minimal fax mode described in <a href="#section-3">Section</a>
   <a href="#section-3">3</a>) SHOULD NOT use these fields. Recommended fields that are mode-
   specific are described in Sections <a href="#section-3">3</a>-<a href="#section-8">8</a>.

DateTime(306)                                                      ASCII
    OptionalInTIFFBaseline
    Date/time of image creation in 24-hour format "YYYY:MM:DD HH:MM:SS".
    No default.

DocumentName(269)                                                  ASCII
    OptionalInTIFFExtension(DocumentStorageAndRetrieval)
    The name of the scanned document. This is a TIFF extension field,
    not a Baseline TIFF field.



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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


    No default.

ImageDescription(270)                                              ASCII
    OptionalInTIFFBaseline
    A string describing the contents of the image.
    No default.

Orientation(274) = 1-8.                                            SHORT
    OptionalinTIFFBaseline
    1: 0th row represents the visual top of the image; the 0th column
    represents the visual left side of the image. See the current TIFF
    spec [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] for further values; Baseline TIFF only requires value=1.
    Default = 1.
    Note: It is recommended that a writer that is aware of the
    orientation will include this field to give a positive indication of
    the orientation, even if the value is the default. If the
    Orientation field is omitted, the reader SHALL assume a value of 1.

Software(305)                                                      ASCII
    OptionalInTIFFBaseline
    The optional name and release number of the software package that
    created the image.
    No default.

<span class="h4"><a class="selflink" id="section-2.2.4" href="#section-2.2.4">2.2.4</a> New TIFF fields recommended for fax modes</span>

   The new TIFF fields listed in this section MAY be used by all fax
   modes, but their support is not expected for the minimal fax mode
   described in <a href="#section-3">Section 3</a>. In addition, support for these new TIFF
   fields has not been included in historical TIFF-F readers described
   in <a href="#section-4">Section 4</a> and [TIFF- F]. These fields describe "global" parameters
   of the fax session that created the image data. They are optional,
   not part of the current TIFF specification, and are defined in this
   document.

   The first new field, GlobalParametersIFD, is an IFD that contains
   global parameters and is located in a Primary IFD.

GlobalParametersIFD (400)                                            IFD
    An IFD containing global parameters. It is recommended that a TIFF
    writer place this field in the first IFD, where a TIFF reader would
    find it quickly.

   Each field in the GlobalParametersIFD is a TIFF field that is legal
   in any IFD. Required baseline fields should not be located in the
   GlobalParametersIFD, but should be in each image IFD. If a conflict
   exists between fields in the GlobalParametersIFD and in the image
   IFDs, then the data in the image IFD shall prevail.



<span class="grey">McIntyre, et. al.           Standards Track                    [Page 16]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-17" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   Among the GlobalParametersIFD entries is a new ProfileType field
   which generally describes information in this IFD and in the TIFF
   file.

ProfileType(401)                                                    LONG
    The type of image data stored in this IFD.
    0 = Unspecified
    1 = Group 3 fax
    No default

   The following new global fields are defined in this document as IFD
   entries for use with fax applications.

FaxProfile(402) = 0 - 6.                                            BYTE
    The profile that applies to this file; a profile is subset of the
    full set of permitted fields and field values of TIFF for facsimile.
    The currently defined values are:
    0: does not conform to a profile defined for TIFF for facsimile
    1: minimal black &amp; white lossless, Profile S
    2: extended black &amp; white lossless, Profile F
    3: lossless JBIG black &amp; white, Profile J
    4: lossy color and grayscale, Profile C
    5: lossless color and grayscale, Profile L
    6: Mixed Raster Content, Profile M

CodingMethods(403)                                                  LONG
    This field indicates which coding methods are used in the file. A
    bit value of 1 indicates which of the following coding methods is
    used:
    Bit 0: unspecified compression,
    Bit 1: 1-dimensional coding, ITU-T Rec. T.4 (MH - Modified Huffman),
    Bit 2: 2-dimensional coding, ITU-T Rec. T.4 (MR - Modified Read),
    Bit 3: 2-dimensional coding, ITU-T Rec. T.6 (MMR - Modified MR),
    Bit 4: ITU-T Rec. T.82 coding, using ITU-T Rec. T.85 (JBIG),
    Bit 5: ITU-T Rec. T.81 (Baseline JPEG),
    Bit 6: ITU-T Rec. T.82 coding, using ITU-T Rec. T.43 (JBIG color),
    Bits 7-31: reserved for future use
    Note: There is a limit of 32 compression types to identify standard
    compression methods.

VersionYear(404)                                                    BYTE
    Count: 4
    The year of the standard specified by the FaxProfile field, given as
    4 characters, e.g. '1997'; used in lossy and lossless color modes.

ModeNumber (405)                                                    BYTE
    The mode of the standard specified by the FaxProfile field. A
    value of 0 indicates Mode 1.0; used in Mixed Raster Content mode.



<span class="grey">McIntyre, et. al.           Standards Track                    [Page 17]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-18" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Minimal Black-and-White Fax Mode</span>

   This section defines the minimal black-and-white subset of TIFF for
   facsimile. This subset is designated Profile S. All implementations
   of TIFF for facsimile SHALL support the minimal subset.

   Black-and-white mode is the binary fax application most users are
   familiar with today. This mode is appropriate for black-and-white
   text and line art. Black-and-white mode is divided into two levels of
   capability. This section describes the minimal interchange set of
   TIFF fields that must be supported by all implementations in order to
   assure that some form of image, albeit black-and-white, can be
   interchanged. This minimum interchange set is a strict subset of the
   fields and values defined for the extended black-and-white mode
   (TIFF-F or Profile F) in <a href="#section-4">Section 4</a>, which describes extensions to the
   minimal interchange set of fields that provide a richer set of
   black-and-white capabilities.

<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>. Overview</span>

   The minimal interchange portion of the black-and-white facsimile mode
   supports 1-dimensional Modified Huffman (MH) compression, with the
   original Group 3 fax resolutions, commonly called "standard" and
   "fine."

   To assure interchange, this mode uses the minimal set of fields, with
   a minimal set of values. There are no recommended fields in this
   mode. Further, the TIFF file is required to be "little endian," which
   means that the byte order value in the TIFF header is "II". This mode
   defines a required ordering for the pages in a fax document and for
   the IFDs and image data of a page. It also requires that a single
   strip contain the image data for each page; see <a href="#section-3.5">Section 3.5</a>. The
   image data may contain RTC sequences, as specified in <a href="#section-3.4">Section 3.4</a>.

<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>. Required TIFF Fields</span>

   Besides the fields listed in <a href="#section-2.2.1">Section 2.2.1</a>, the minimal black-and-
   white fax mode requires the following fields. The fields listed in
   <a href="#section-2.2.1">Section 2.2.1</a> and the fields and fax-specific values specified in
   this sub- section must be supported by all implementations.

<span class="h4"><a class="selflink" id="section-3.2.1" href="#section-3.2.1">3.2.1</a> Baseline fields</span>

BitsPerSample(258) = 1.                                            SHORT
    RequiredByTIFFBaseline
    Binary data only.
    Default = 1 (field may be omitted if this is the value)




<span class="grey">McIntyre, et. al.           Standards Track                    [Page 18]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-19" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


Compression(259) = 3.                                              SHORT
    RequiredByTIFFBaseline
    3 = 1- or 2- dimensional coding.
    The value 3 is a TIFF extension value [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>]. The T4Options field
    must be specified and its value specifies that the data is encoded
    using the Modified Huffman (MH) encoding of [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>].

FillOrder(266) = 2.                                                SHORT
    RequiredByTIFFBaseline
    2 = Least Significant Bit first

   NOTE: Baseline TIFF readers are only required to support FillOrder =
   1, where the lowest numbered pixel is stored in the MSB of the byte.
   However, because many devices, such as modems, transmit the LSB first
   when converting the data to serial form, it is common for black-and-
   white fax products to use the second FillOrder =2, where the lowest
   numbered pixel is stored in the LSB. Therefore, this value is
   specified in the minimal black-and-white mode.

ImageWidth(256) = 1728.                                    SHORT or LONG
    RequiredByTIFFBaseline
    This mode only supports a page width of 1728 pixels. This width
    corresponds to North American Letter and Legal and to ISO A4 size
    pages.
    No default, must be specified.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

PhotometricInterpretation(262) = 0.                                SHORT
    RequiredByTIFFBaseline
    0 = pixel value 1 means black
    No default, must be specified

ResolutionUnit(296) = 2.                                           SHORT
    RequiredByTIFFBaseline
    The unit of measure for resolution. 2 = inch.
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277) = 1.                                          SHORT
    RequiredByTIFFBaseline
    The number of components per pixel; 1 for black-and-white
    Default =1 (field may be omitted if this is the value)

XResolution(282) = 200, 204.                                    RATIONAL
    RequiredByTIFFBaseline



<span class="grey">McIntyre, et. al.           Standards Track                    [Page 19]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-20" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


    The horizontal resolution of the image is expressed in pixels per
    resolution unit. In pixels/inch, the allowed values are 200 and 204,
    which may be treated as equivalent. See <a href="#section-2.2.2">Section 2.2.2</a> for inch-
    metric equivalency.
    No default, must be specified

YResolution(283) = 98, 100, 196, 200.                           RATIONAL
    RequiredByTIFFBaseline
    The vertical resolution of the image is expressed in pixels per
    resolution unit. In pixels/inch, the allowed values are 98, 100,
    196 and 200; 98 and 100 may be treated as equivalent, and 196 and
    200 may be treated as equivalent. See <a href="#section-2.2.2">Section 2.2.2</a> for inch-metric
    equivalency.
    No default, must be specified

<span class="h4"><a class="selflink" id="section-3.2.2" href="#section-3.2.2">3.2.2</a> Extension fields</span>

T4Options(292) = (Bit 0 = 0, Bit 1 = 0, Bit 2 = 0, 1)               LONG
    RequiredTIFFExtension (when Compression = 3)
    Bit 0 = 0 indicates MH encoding.
    Bit 1 must be 0
    Bit 2 = 1 indicates that EOLs are byte aligned, = 0 EOLs not byte
    aligned
    Default is all bits are 0 (applies when EOLs are not byte aligned)

   Note: The T4Options field is required when the Compression field has
   a value of 3. Bit 0 of this field specifies the encoding used (MH
   only in this mode) and Bit 2 indicates whether the EOL codes are
   byte-aligned or not. If they are byte aligned, then fill bits have
   been added as necessary so that the End of Line (EOL) codes always
   end on byte boundaries. See <a href="#section-3.4">Section 3.4</a> for details.

<span class="h4"><a class="selflink" id="section-3.2.3" href="#section-3.2.3">3.2.3</a>. New Fields</span>

   None.

<span class="h3"><a class="selflink" id="section-3.3" href="#section-3.3">3.3</a>. Recommended TIFF Fields</span>

   None.

<span class="h3"><a class="selflink" id="section-3.4" href="#section-3.4">3.4</a>. End of Line (EOL) and Return to Control (RTC)</span>

   The handling of End of Line (EOL) codes and Return to Control (RTC)
   sequences illustrate the differences between conventional fax, which
   is bit and stream oriented, and TIFF, which is byte and file
   oriented. Conventional fax, Baseline TIFF and TIFF extensions for fax
   all handle EOLs and RTCs differently.




<span class="grey">McIntyre, et. al.           Standards Track                    [Page 20]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-21" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   In conventional fax, an MH-compressed fax data stream for a page
   consists of the following sequence:

      EOL, compressed data (first line), EOL, compressed data, ... ,
      EOL, compressed data (last line), RTC (6 consecutive EOL codes)

   Baseline TIFF does not use EOL codes or Return to Control (RTC)
   sequences for MH-compressed data. However, the TIFF extension field
   T4Options used in this specification for MH compression (Compression
   = 3) requires EOLs.

   Furthermore, Bit 2 in the T4Options field indicates whether or not
   the EOL codes are byte aligned. If Bit 2 = 1, indicating the EOL
   codes are byte aligned, then fill bits have been added as necessary
   before EOL codes so that an EOL code always ends on a byte boundary,
   and the first bit of data following an EOL begins on a byte boundary.
   Without fill bits, an EOL code may end in the middle of a byte. Byte
   alignment relieves application software of the burden of bit-shifting
   every byte while parsing scan lines for line-oriented image
   manipulation (such as writing a TIFF file). Not all TIFF readers
   historically used for fax are able to deal with non-byte aligned
   data.

   While TIFF extension requires EOL codes, TIFF in fax applications has
   traditionally prohibited RTC sequences. Implementations that want
   common processing and interfaces for fax data streams and Internet
   fax files would prefer that the TIFF data include RTC sequences.

   To reconcile these differences, RTCs are allowed in cases where EOL
   codes are not byte aligned and no fill bits have been added to the
   data. This corresponds to situations where the fax data is simply
   inserted in a strip without being processed or interpreted. RTCs
   should not occur in the data when EOLs have been byte aligned. This
   is formally specified in the next sub-section.

<span class="h4"><a class="selflink" id="section-3.4.1" href="#section-3.4.1">3.4.1</a>. RTC Exclusion</span>

   Implementations which wish to maintain strict conformance with TIFF
   and compatibility with the historical use of TIFF for fax SHOULD NOT
   include the RTC sequence when writing TIFF files. However,
   implementations which need to support "transparency" of T.4-generated
   image data MAY include RTCs when writing TIFF files if the flag
   settings of the T4Options field are set for non-byte aligned data,
   i.e. Bit 2 is 0. Implementors of TIFF readers should be aware that
   there are some existing TIFF implementations for fax that include the
   RTC sequence in MH image data. Therefore, minimal set readers MUST be
   able to process files which do not include RTCs and SHOULD be able to
   process files which do include RTCs.



<span class="grey">McIntyre, et. al.           Standards Track                    [Page 21]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-22" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


<span class="h3"><a class="selflink" id="section-3.5" href="#section-3.5">3.5</a>. File Structure</span>

   The TIFF header, described in <a href="#section-2.1.1">Section 2.1.1</a>, contains two bytes which
   describe the byte order used within the file. For the minimal black-
   and- white mode, these bytes SHALL have the value "II" (0x4949),
   denoting that the bytes in the TIFF file are in LSByte-first order
   (little- endian). The first or 0th IFD immediately follows the
   header, so that offset to the first IFD is 8. The headers values are
   shown in the following table:

          +--------+-------------------+--------+-----------+
          | Offset |   Description     |     Value          |
          +--------+-------------------+--------+-----------+
          |   0    |   Byte Order      |  0x4949 (II)       |
          +--------+-------------------+--------+-----------+
          |   2    |   Identifier      |  42 decimal        |
          +--------+-------------------+--------+-----------+
          |   4    | Offset of 0th IFD |  0x 0000 0008      |
          +--------+-------------------+--------+-----------+

   The minimal black-and-white mode SHALL order IFDs and image data
   within a file as follows: 1) there SHALL be an IFD for each page in a
   multi- page fax document; (2) the IFDs SHALL occur in the same order
   in the file as the pages occur in the document; (3) the IFD SHALL
   precede the image data to which it has offsets; (4) the image data
   SHALL occur in the same order in the file as the pages occur in the
   document; (5) the IFD, the value data and the image data it has
   offsets to SHALL precede the next image IFD; and (6) the image data
   for each page SHALL be contained within a single strip.

   As a result of (6), the StripOffsets field will contain the pointer
   to the image data. With two exceptions, the field entries in the IFD
   contain the field values instead of offsets to field values located
   outside the IFD. The two exceptions are the values for the
   XResolution and YResolution fields, both of which are type RATIONAL
   and require 2 4- byte numbers. These "long" field values SHALL be
   placed immediately after  the IFD which contains the offsets to them,
   and before the image data pointed to by that IFD.

   The effect of these requirements is that the IFD for the first page
   SHALL come first in the file after the TIFF header, followed by the
   long field values for XResolution and YResolution, followed by the
   image data for the first page, then the IFD for second page, etc.
   This is shown in the following figure. Each IFD is required to have a
   PageNumber field, which has value 0 for the first page, 1 for the
   second page, and so on.





<span class="grey">McIntyre, et. al.           Standards Track                    [Page 22]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-23" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


                   +-----------------------+
                   |         Header        |------------+
                   +-----------------------+            | First IFD
                   |      IFD (page 0)     | &lt;----------+ Offset
               +---|                       |------------+
               |   |                       |--+         |
         Value |   +-----------------------+  |         |
        Offset +--&gt;|      Long Values      |  |         |
                   +-----------------------|  | Strip   |
                   |  Image Data (page 0)  |&lt;-+ Offset  |
                   +-----------------------+            | Next IFD
                   |      IFD (page 1)     | &lt;----------+ Offset
               +---|                       |------------+
               |   |                       |--+         |
         Value |   +-----------------------+  |         |
        Offset +--&gt;|      Long Values      |  |         |
                   +-----------------------|  | Strip   |
                   |  Image Data (page 1)  |&lt;-+ Offset  |
                   +-----------------------+            | Next IFD
                   |      IFD (page 2)     | &lt;----------+ Offset
                   +-----------------------+
                   |          :            |

   Using this file structure may reduce the memory requirements in
   implementations. It is also provides some support for streaming, in
   which a file can be processed as it is received and before the entire
   file is received.

<span class="h3"><a class="selflink" id="section-3.6" href="#section-3.6">3.6</a> Minimal Black-and-white Mode Summary</span>

   The table below summarizes the TIFF fields that comprise the minimal
   interchange set for black-and-white facsimile. The Baseline and
   Extension fields and field values MUST be supported by all
   implementations. For convenience in the table, certain fields which
   have a value that is a sequence of flag bits are shown taking integer
   values that correspond to the flags that are set. An implementation
   should test the setting of the relevant flag bits individually,
   however, to allow extensions to the sequence of flag bits to be
   appropriately ignored. (See, for example, T4Options below.)

      +---------------------------+--------------------------------+
      | Baseline Fields           |  Values                        |
      +---------------------------+--------------------------------+
      | BitsPerSample             | 1                              |
      +---------------------------+--------------------------------+
      | Compression               | 3: 1D Modified Huffman coding  |
      |                           |     set T4Options = 0 or 4     |
      +------------------------------------------------------------+



<span class="grey">McIntyre, et. al.           Standards Track                    [Page 23]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-24" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


      +---------------------------+--------------------------------+
      | FillOrder                 | 2: least significant bit first |
      +---------------------------+--------------------------------+
      | ImageWidth                | 1728                           |
      +---------------------------+--------------------------------+
      | ImageLength               | n: total number of scanlines   |
      |                           | in image                       |
      +---------------------------+--------------------------------+
      | NewSubFileType            | 2: Bit 1 identifies single     |
      |                           | page of a multi-page document  |
      +---------------------------+--------------------------------+
      | PageNumber                | n,m: page number n followed by |
      |                           | total page count m             |
      +---------------------------+--------------------------------+
      | PhotometricInterpretation | 0: pixel value 1 means black   |
      +---------------------------+--------------------------------+
      | ResolutionUnit            | 2: inch                        |
      +---------------------------+--------------------------------+
      | RowsPerStrip              | number of scanlines per strip  |
      |                           | = ImageLength, with one strip  |
      +---------------------------+--------------------------------+
      | SamplesPerPixel           | 1                              |
      +---------------------------+--------------------------------+
      | StripByteCounts           | number of bytes in TIFF strip  |
      +---------------------------+--------------------------------+
      | StripOffsets              | offset from beginning of       |
      |                           | file to single TIFF strip      |
      +---------------------------+--------------------------------+
      | XResolution               | 204, 200 (pixels/inch)         |
      +---------------------------+--------------------------------+
      | YResolution               | 98, 196, 100, 200 (pixels/inch)|
      +---------------------------+--------------------------------+
      | Extension Fields                                           |
      +---------------------------+--------------------------------+
      | T4Options                 | 0: MH coding, EOLs not byte    |
      |                           |               aligned          |
      |                           | 4: MH coding, EOLs byte aligned|
      +---------------------------+--------------------------------+

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Extended Black-and-White fax mode</span>

   This section defines the extended black-and-white mode or Profile F
   of TIFF for facsimile. It provides a standard definition of what has
   historically been known as TIFF Class F and now TIFF-F. In doing so,
   it aligns this mode with current ITU-T Recommendations for black-
   and-white fax and with existing industry practice. Implementations of
   this profile include implementations of Profile S.




<span class="grey">McIntyre, et. al.           Standards Track                    [Page 24]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-25" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   This section describes extensions to the minimal interchange set of
   fields (Profile S) that provide a richer set of black-and-white
   capabilities. The fields and values described in this section are a
   superset of the fields and values defined for the minimal interchange
   set in <a href="#section-3">Section 3</a>. In addition to the MH encoding, Modified READ (MR)
   and Modified Modified READ (MMR) encoding as described in [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>] and
   [<a href="#ref-T.6" title="Facsimile coding schemes and coding control functions for group 4 facsimile apparatus">T.6</a>] are supported.

   <a href="#section-4.1">Section 4.1</a> gives an overview of TIFF-F. <a href="#section-4.2">Section 4.2</a> describes the
   TIFF fields that SHALL be used in this mode. <a href="#section-4.3">Section 4.3</a> describes
   the fields that MAY be used in this mode. In the spirit of the
   original TIFF-F specification, Sections <a href="#section-4.4">4.4</a> and <a href="#section-4.5">4.5</a> discuss technical
   implementation issues and warnings. <a href="#section-4.6">Section 4.6</a> gives an example use
   of TIFF-F. <a href="#section-4.7">Section 4.7</a> gives a summary of the required and
   recommended fields and their values.

<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a> TIFF-F Overview</span>

   Though it has been in common usage for many years, TIFF-F has
   previously never been documented in the form of a standard.  An
   informal TIFF-F document was originally created by a small group of
   fax experts led by Joe Campbell.  The existence of TIFF-F is noted in
   [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] but it is not defined.  This document serves as the formal
   definition of the F application of [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] for Internet applications.
   For ease of reference, the term TIFF-F will be used throughout this
   document as a shorthand for the extended black-and-white mode or
   profile of TIFF for facsimile.

   Up until the TIFF 6.0 specification, TIFF supported various "Classes"
   which defined the use of TIFF for various applications. Classes were
   used to support specific applications. In this spirit, TIFF-F has
   been known historically as "TIFF Class F".  Previous informal TIFF-F
   documents [<a href="#ref-TIFF-F0" title="1990">TIFF-F0</a>] used the "Class F" terminology.  As of TIFF 6.0
   [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>], the TIFF Class concept has been eliminated in favor of the
   concept of Baseline TIFF.  Therefore, this document updates the
   definition of TIFF-F as the F profile of TIFF for facsimile, by using
   Baseline  TIFF as defined in [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] as the starting point and then
   adding the TIFF extensions to Baseline TIFF which apply for TIFF-F.
   In almost all  cases, the resulting definition of TIFF-F fields and
   values remains  consistent with those used historically in earlier
   definitions of TIFF  Class F.  Where some of the values for fields
   have been updated to provide more precise conformance with the ITU-T
   [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>] and [<a href="#ref-T.30">T.30</a>] fax recommendations, these differences are noted.








<span class="grey">McIntyre, et. al.           Standards Track                    [Page 25]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-26" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>. Required TIFF Fields</span>

   This section lists the required fields and the values they must have
   to be ITU-compatible. Besides the fields listed in <a href="#section-2.2.1">Section 2.2.1</a>, the
   extended black-and-white fax mode SHALL use the following fields.

<span class="h4"><a class="selflink" id="section-4.2.1" href="#section-4.2.1">4.2.1</a>. Baseline fields</span>

BitsPerSample(258) = 1.                                            SHORT
    RequiredByTIFFBaseline
    Binary data only.
    Default = 1 (field may be omitted if this is the value)

Compression(259) = 3, 4.                                           SHORT
    RequiredByTIFFBaseline
    3 = 1- or 2- dimensional coding, must have T4Options field This is
    a TIFF Extension value [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>].
    4 = 2-dimensional coding, ITU-T Rec. T.6 (MMR - Modified Modified
    Read, must have T6Options field)) This is a TIFF Extension value.
    Default = 1 (and is not applicable; field must be specified)

   NOTE: Baseline TIFF permits use of value 2 for Modified Huffman
   encoding, but data is presented in a form which does not use EOLs,
   and so TIFF for facsimile uses Compression=3 instead. See Sections
   4.4.4, 4.5.1 and 4.5.2 for more information on compression and
   encoding.

FillOrder(266) = 1 , 2.                                            SHORT
    RequiredByTIFFBaseline
    Profile F readers must be able to read data in both bit orders,
    but the vast majority of facsimile products store data LSB
    first, exactly as it appears on the telephone line.
              1 = Most Significant Bit first.
              2 = Least Significant Bit first

ImageWidth(256)                                            SHORT or LONG
    RequiredByTIFFBaseline
    This mode supports the following fixed page widths: 1728, 2592, 3456
    (corresponding to North American Letter and Legal, ISO A4 paper
    sizes), 2048, 3072, 4096 (corresponding to ISO B4 paper size), and
    2432, 3648, 4864 (corresponding to ISO A3 paper size).
    No default; must be specified

   NOTE: Historical TIFF-F did not include support for the following
   widths related to higher resolutions: 2592, 3072, 3648, 3456, 4096
   and 4864. Historical TIFF-F documents also included the following
   values related to A5 and A6 widths: 816 and 1216. Per the most recent




<span class="grey">McIntyre, et. al.           Standards Track                    [Page 26]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-27" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   version of [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>], A5 and A6 documents are no longer supported in
   Group 3 facsimile, so the related width values are now obsolete. See
   <a href="#section-4.5.2">section 4.5.2</a> for more information on inch/metric equivalencies and
   other implementation details.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

   NOTE: Bit 1 is always set to 1 for TIFF-F, indicating a single page
   of a multi-page image. The same bit settings are used when TIFF-F is
   used for a one page fax image. See <a href="#section-4.4.3">Section 4.4.3</a> for details on
   multi-page files.

PhotometricInterpretation(262) = 0, 1.                             SHORT
    RequiredByTIFFBaseline
    0 = pixel value 1 means black, 1 = pixel value 1 means white.
    This field allows notation of an inverted or negative image.
    No default, must be specified

ResolutionUnit(296) = 2, 3.                                        SHORT
    RequiredByTIFFBaseline
    The unit of measure for resolution. 2 = inch, 3 = centimeter; TIFF-F
    has traditionally used inch-based measures.
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277) = 1.                                          SHORT
    RequiredByTIFFBaseline
    1 = monochrome, bilevel in this case (see BitsPerSample)
    Default =1 (field may be omitted if this is the value)

XResolution(282) = 200, 204, 300, 400, 408                      RATIONAL
    RequiredByTIFFBaseline
    The horizontal resolution of the image is expressed in pixels per
    resolution unit. In pixels/inch, the allowed values are: 200, 204,
    300, 400, and 408. See <a href="#section-2.2.2">Section 2.2.2</a> for inch-metric equivalency.
    No default, must be specified

   NOTE: The values of 200 and 408 have been added to the historical
   TIFF-F values, for consistency with [<a href="#ref-T.30">T.30</a>]. Some existing TIFF-F
   implementations may also support values of 80 pixels/cm, which is
   equivalent to 204 pixels per inch. See <a href="#section-4.5.2">section 4.5.2</a> for information
   on implementation details.

YResolution(283) = 98, 100, 196, 200, 300, 391, and 400       RATIONAL
    RequiredByTIFFBaseline
    The vertical resolution of the image is expressed in pixels per



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    resolution unit. In pixels/inch, the allowed values are: 98, 100,
    196, 200, 300, 391, and 400 pixels/inch.
    See <a href="#section-2.2.2">Section 2.2.2</a> for inch-metric equivalency.
    No default, must be specified

   NOTE: The values of 100, 200, and 391 have been added to the
   historical TIFF-F values, for consistency with [<a href="#ref-T.30">T.30</a>].  Some existing
   TIFF-F implementations may also support values of 77 and 38.5 (cm),
   which are equivalent to 196 and 98 pixels per inch respectively. See
   <a href="#section-4.5.2">section 4.5.2</a> for more information on implementation details.

   NOTE: Not all combinations of XResolution, YResolution and ImageWidth
   are legal. The following table gives the legal combinations and
   corresponding paper size [<a href="#ref-T.30">T.30</a>].

    +--------------+-----------------+---------------------------+
    |   XResolution x YResolution    |         ImageWidth        |
    +--------------+-----------------+---------+--------+--------+
    |      200x100, 204x98           |         |        |        |
    |      200x200, 204x196          |  1728   |  2048  |  2432  |
    |           204x391              |         |        |        |
    +--------------+-----------------+---------+--------+--------+
    |          300 x 300             |  2592   |  3072  |  3648  |
    +--------------+-----------------+---------+--------+--------+
    |     408 x 391, 400 x 400       |  3456   |  4096  |  4864  |
    +--------------+-----------------+---------+--------+--------+
                                     |Letter,A4|   B4   |   A3   |
                                     |  Legal  |        |        |
                                     +---------+--------+--------+
                                     |         Paper Size        |
                                     +---------------------------+


<span class="h4"><a class="selflink" id="section-4.2.2" href="#section-4.2.2">4.2.2</a>. Extension fields</span>

T4Options(292) = (Bit 0 = 0 or 1, Bit 1 = 0, Bit 2 = 0 or 1)        LONG
    RequiredTIFFExtension (when Compression = 3)
    T4Options was also known as Group3Options in a prior version of
    [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>].
    Bit 0 = 1 indicates MR encoding, = 0 indicates MH encoding.
    Bit 1 must be 0
    Bit 2 = 1 indicates that EOLs are byte aligned, = 0 EOLs not byte
    aligned
    Default is all bits are 0 (applies when MH encoding is used and EOLs
    are not byte aligned EOLs) (See <a href="#section-3.2.2">Section 3.2.2</a>.)
    The T4Options field is required when the Compression field has a
    value of 3. This field specifies the encoding used (MH or MR) and
    whether the EOL codes are byte-aligned or not. If they are byte



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    aligned, then fill bits have been added as necessary so that the End
    of Line (EOL) codes always end on byte boundaries See Sections <a href="#section-3.4">3.4</a>,
    4.5.3 and 4.5.4 for details.

T6Options(293) = (Bit 0 = 0, Bit 1 = 0). LONG
    RequiredTIFFExtension (when Compression = 4)
    Used to indicate parameterization of 2D Modified Modified Read
    compression. T6Options was also known as Group4Options in a prior
    version of [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>].
    Bit 0 must be 0.
    Bit 1 = 0 indicates uncompressed data mode is not allowed; = 1
    indicates uncompressed data is allowed (see [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>]).
    Default is all bits 0. For FAX, the field must be present and have
    the value 0. The use of uncompressed data where compression would
    expand the data size is not allowed for FAX.

   NOTE: MMR compressed data is two-dimensional and does not use EOLs.
   Each MMR encoded image MUST include an "end-of-facsimile-block"
   (EOFB) code at the end of each coded strip; see <a href="#section-4.5.6">Section 4.5.6</a>.

<span class="h4"><a class="selflink" id="section-4.2.3" href="#section-4.2.3">4.2.3</a>. New fields</span>

   None.

<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a>. Recommended TIFF fields</span>

<span class="h4"><a class="selflink" id="section-4.3.1" href="#section-4.3.1">4.3.1</a>. Baseline fields</span>

   See <a href="#section-2.2.3">Section 2.2.3</a>.

<span class="h4"><a class="selflink" id="section-4.3.2" href="#section-4.3.2">4.3.2</a>. Extension fields</span>

   See <a href="#section-2.2.3">Section 2.2.3</a>.

<span class="h4"><a class="selflink" id="section-4.3.3" href="#section-4.3.3">4.3.3</a>. New fields</span>

   Three new, optional fields, used in the original TIFF-F description
   to describe page quality, are defined in this specification.  The
   information contained in these fields is usually obtained from
   receiving facsimile hardware (if applicable). They SHOULD NOT be used
   in writing TIFF-F files for facsimile image data that is error
   corrected or otherwise guaranteed not to have coding errors. Some
   applications need to understand exactly the error content of the
   data.  For example, a CAD program might wish to verify that a  file
   has a low error level before importing it into a high-accuracy
   document. Because Group 3 facsimile devices do not necessarily
   perform error correction on the image data, the quality of a received
   page must be inferred from the pixel count of decoded scan lines. A



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   "good" scan line is defined as a line that, when decoded, contains
   the correct number of pixels. Conversely, a "bad" scan line is
   defined as a line that, when decoded, comprises an incorrect number
   of pixels.

BadFaxLines(326)                                           SHORT or LONG
    The number of "bad" scan lines encountered by the facsimile device
    during reception. A "bad" scanline is defined as a scanline that,
    when decoded, comprises an incorrect number of pixels. Note that
    PercentBad = (BadFaxLines/ImageLength) * 100
    No default.

CleanFaxData(327) = 0, 1, 2.                                       SHORT
    Indicates if "bad" lines encountered during reception are stored in
    the data, or if "bad" lines have been replaced by the receiver.
    0 = No "bad" lines
    1 = "bad" lines exist, but were regenerated by the receiver,
    2 = "bad" lines exist, but have not been regenerated.
    No default.

   NOTE: Many facsimile devices do not actually output bad lines.
   Instead, the previous good line is repeated in place of a bad line.
   Although this substitution, known as line regeneration, results in a
   visual improvement to the image, the data is nevertheless corrupted.
   The CleanFaxData field describes the error content of the data.  That
   is, when the BadFaxLines and ImageLength fields indicate that the
   facsimile device encountered lines with an incorrect number of pixels
   during reception, the CleanFaxData field indicates whether these bad
   lines are actually still in the data or if the receiving facsimile
   device replaced them with regenerated lines.

ConsecutiveBadFaxLines(328)                               LONG or SHORT
    Maximum number of consecutive "bad" scanlines received.  The
    BadFaxLines field indicates only the quantity of bad lines.
    No Default.

   NOTE: The BadFaxLines and ImageLength data indicate only the quantity
   of bad lines. The ConsecutiveBadFaxLines field is an indicator of the
   distribution of bad lines and may therefore be a better general
   indicator of perceived image quality. See <a href="#section-4.4.5">Section 4.4.5</a> for examples
   of the use of these fields.

<span class="h3"><a class="selflink" id="section-4.4" href="#section-4.4">4.4</a>. Technical Implementation Issues</span>

<span class="h4"><a class="selflink" id="section-4.4.1" href="#section-4.4.1">4.4.1</a>   Strips</span>

   In general, TIFF files divide an image into "strips," also known as
   "bands."  Each strip contains a few scanlines of the image. By using



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   strips, a TIFF reader need not load the entire image into memory,
   thus enabling it to fetch and decompress small random portions of the
   image as necessary.

   The number of scanlines in a strip is described by the RowsPerStrip
   value and the number of bytes in the strip after compression by the
   StripByteCount value.  The location in the TIFF file of each strip is
   given by the StripOffsets values.

   Strip size is application dependent. The recommended approach for
   multi- page TIFF-F images is to represent each page as a single
   strip. Existing TIFF-F usage is typically one strip per page in
   multi-page TIFF-F files. See Sections <a href="#section-2.1.2">2.1.2</a> and <a href="#section-2.1.3">2.1.3</a>.

<span class="h4"><a class="selflink" id="section-4.4.2" href="#section-4.4.2">4.4.2</a>  Bit Order</span>

   The current TIFF specification [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] does not require a Baseline
   TIFF reader to support FillOrder=2, i.e. lowest numbered 1-bit pixel
   in the least significant bit of a byte. It further recommends that
   FillOrder=2 be used only in special purpose applications.

   Facsimile data appears on the phone line in bit-reversed order
   relative to its description in ITU-T Recommendation T.4.  Therefore,
   a wide majority of facsimile applications choose this natural order
   for data in a file. Nevertheless, TIFF-F readers must be able to read
   data in both bit orders and support FillOrder values of 1 and 2.

<span class="h4"><a class="selflink" id="section-4.4.3" href="#section-4.4.3">4.4.3</a>. Multi-Page</span>

   Many existing applications already read TIFF-F-like files, but do not
   support the multi-page field.  Since a multi-page format greatly
   simplifies file management in fax application software, TIFF-F
   specifies multi-page documents (NewSubfileType = 2) as the standard
   case.

   It is recommended that applications export multiple page TIFF-F files
   without manipulating fields and values.   Historically, some TIFF-F
   writers have attempted to produce individual single-page TIFF-F files
   with modified NewSubFileType and PageNumber (page one-of-one) values
   for export purposes.  However, there is no easy way to link such
   multiple single page files together into a logical multiple page
   document, so that this practice is not recommended.

<span class="h4"><a class="selflink" id="section-4.4.4" href="#section-4.4.4">4.4.4</a>. Compression</span>

   In Group 3 facsimile, there are three compression methods which had
   been standardized as of 1994 and are in common use. The ITU-T T.4
   Recommendation [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>] defines a one-dimensional compression method



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   known as Modified Huffman (MH) and a two-dimensional method known as
   Modified READ (MR) (READ is short for Relative Element Address
   Designate). In 1984, a somewhat more efficient compression method
   known as Modified Modified READ (MMR) was defined in the ITU-T T.6
   Recommendation [<a href="#ref-T.6" title="Facsimile coding schemes and coding control functions for group 4 facsimile apparatus">T.6</a>]. MMR was originally defined for use with Group 4
   facsimile, so that this compression method has been commonly called
   Group 4 compression.  In 1991, the MMR method was approved for use in
   Group 3 facsimile and has since been widely utilized.

   TIFF-F supports these three compression methods. The most common
   practice is the one-dimensional Modified Huffman (MH) compression
   method.  This is specified by setting the Compression field value to
   3 and then setting bit 0 of the T4Options field to 0.  Alternatively,
   the two dimensional Modified READ (MR) method, which is much less
   frequently used in historical TIFF-F implementations, may be selected
   by setting bit 0 of the T4Options field to 1.  The value of Bit 2 in
   this field is determined by the use of fill bits.

   Depending upon the application, the more efficient two-dimensional
   Modified Modified Read (MMR)compression method from T.6 may be
   selected by setting the Compression field value to 4 and then setting
   the first two bits (and all unused bits) of the T6Options field to 0.
   More information to aid the implementor in making a compression
   selection is contained in <a href="#section-4.5.2">Section 4.5.2</a>.

   Baseline TIFF also permits use of Compression=2 to specify Modified
   Huffman compression, but the data does not use EOLs. As a result,
   TIFF-F uses Compression=3 instead of Compression=2 to specify
   Modified Huffman compression.

<span class="h4"><a class="selflink" id="section-4.4.5" href="#section-4.4.5">4.4.5</a>.  Example Use of Page-quality Fields</span>

   Here are examples for writing the CleanFaxData, BadFaxLines, and
   ConsecutiveBadFaxLines fields:

     1.  Facsimile hardware does not provide page quality
         information: MUST NOT write page-quality fields.
     2.  Facsimile hardware provides page quality information, but
         reports no bad lines.  Write only BadFaxLines = 0.
     3.  Facsimile hardware provides page quality information, and
         reports bad lines.  Write both BadFaxLines and
         ConsecutiveBadFaxLines.  Also write CleanFaxData = 1 or 2 if
         the hardware's regeneration capability is known.
     4.  Source image data stream is error-corrected or otherwise
         guaranteed to be error-free such as for a computer generated
         file:  SHOULD NOT write page-quality fields.





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   TIFF Writers SHOULD only generate these fields when the image has
   been generated from a fax image data stream where error correction,
   e.g. Group 3 Error Correction Mode, was not used.

<span class="h4"><a class="selflink" id="section-4.4.6" href="#section-4.4.6">4.4.6</a>. Practical Guidelines for Writing and Reading Multi-Page TIFF-F</span>
<span class="h4">   Files</span>

   Traditionally, historical TIFF-F has required readers and writers to
   be able to handle multi-page TIFF-F files.  Based on the experience
   of various TIFF-F implementors, it has been seen that the
   implementation of TIFF-F can be greatly simplified if certain
   practical guidelines are followed when writing multi-page TIFF-F
   files.

   The structure for a multi-page TIFF-F file will include one IFD per
   page of the document.  In this case, this IFD will define the
   attributes for a single page. A second simplifying guideline is that
   the writer of TIFF-F files SHOULD present IFDs in the same order as
   the actual sequence of pages.  (The pages are numbered within TIFF-F
   beginning with page 0 as the first page and then ascending (i.e. 0,
   1, 2,...). However, any field values over 4 bytes will be stored
   separately from the IFD. TIFF-F readers SHOULD expect IFDs to be
   presented in page order, but be able to handle exceptions.

   Per [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>], the exact placement of image data is not specified.
   However, the strip offsets for each strip of image are defined from
   within each IFD.   Where possible, another simplifying guideline for
   the writing of TIFF-F files is to specify that the image data for
   each page of a multi-page document SHOULD be contained within a
   single strip (i.e. one image strip per fax page). The use of a single
   image strip per page is very useful for applications such as store
   and forward messaging, where the file is usually prepared in advance
   of the transmission, but other assumptions may apply for the size of
   the image strip for applications which require the use of "streaming"
   techniques (see <a href="#section-4.4.7">section 4.4.7</a>).  In the event a different image strip
   size guideline has been used (e.g. constant size for image strips
   that may be less than the page size), this will immediately be
   evident from the values/offsets of the fields that are related to
   strips.

   A third simplifying guideline is that each IFD SHOULD be placed in
   the TIFF-F file structure at a point which precedes the image which
   the IFD describes.

   In addition, a fourth simplifying guideline for TIFF-F writers and
   readers is to place the actual image data in a physical order within
   the TIFF file structure which is consistent with the logical page
   order.  In practice, TIFF-F readers will need to use the strip



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   offsets to find the exact physical location of the image data,
   whether or not it is presented in logical page order.

   If the image data is stored in multiple strips, then the strips
   SHOULD occur in the file in the same order that the data they contain
   occurs in the facsimile transmission, starting at the top of the
   page.

   TIFF-F writers MAY make a fifth simplifying guideline, in which the
   IFD, the value data and the image data to which the IFD has offsets
   precede the next image IFD. However, this guideline has been relaxed
   (writers MAY rather than SHOULD use it) compared to the other
   guidelines given here to reflect past practices for TIFF-F.

   In the case of the minimal mode, which is also the minimal subset of
   Profile S, the SHOULD's and MAY's of these guidelines become SHALL's
   (see <a href="#section-3.5">Section 3.5</a>).

   So, a TIFF-F file which is structured using the guidelines of this
   section will essentially be composed of a linked list of IFDs,
   presented in ascending page order, which in turn each point to a
   single page of image data (one strip per page), where the pages of
   image data are also placed in a logical page order within the TIFF- F
   file structure.  (The pages of image data may themselves be stored in
   a contiguous manner, at the option of the implementor).

<span class="h4"><a class="selflink" id="section-4.4.7" href="#section-4.4.7">4.4.7</a>.   Use of TIFF-F for Streaming Applications</span>

   TIFF-F has historically been used for handling fax image files in
   applications such as store and forward messaging where the entire
   size of the file is known in advance.  While TIFF-F may also possibly
   be used as a file format for cases such as streaming applications,
   assumptions may be required that differ from those provided in this
   section (e.g., the entire size and number of pages within the image
   are not known in advance).  As a result, a definition for the
   streaming application of TIFF-F is beyond the scope of this document.

<span class="h3"><a class="selflink" id="section-4.5" href="#section-4.5">4.5</a>. Implementation Warnings</span>

<span class="h4"><a class="selflink" id="section-4.5.1" href="#section-4.5.1">4.5.1</a>  Uncompressed data</span>

   TIFF-F requires the ability to read and write at least one-
   dimensional T.4 Huffman ("compressed") data.  Uncompressed data is
   not allowed. This means that the "Uncompressed" bit in T4Options or
   T6Options must be set to 0.






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<span class="h4"><a class="selflink" id="section-4.5.2" href="#section-4.5.2">4.5.2</a>. Encoding and Resolution</span>

   Since two-dimensional encoding is not required for Group 3
   compatibility, some historic TIFF-F readers have not been able to
   read such files.  The minimum subset of TIFF-F REQUIRES support for
   one dimensional (Modified Huffman) files, so this choice maximizes
   portability.  However, implementors seeking greater efficiency SHOULD
   use T.6 MMR compression when writing TIFF-F files.  Some TIFF-F
   readers will also support two-dimensional Modified READ files.
   Implementors that wish to have the maximum flexibility in reading
   TIFF-F files should support all three of these compression methods
   (MH, MR and MMR).

   For the case of resolution, almost all facsimile products support
   both standard (98 dpi) vertical resolution  and "fine" (196 dpi)
   resolution. Therefore, fine-resolution files are quite portable in
   the real world.

   In 1993, the ITU-T added support for higher resolutions in the T.30
   recommendation including 200 x 200, 300 x 300, 400 x 400 in dots per
   inch based units.  At the same time, support was added for metric
   dimensions which are equivalent to the following inch based
   resolutions: 391v x 204h and 391v x 408h.  Therefore, the full set of
   inch-based equivalents of the new resolutions are supported in the
   TIFF-F writer, since they may appear in some image data streams
   received from Group 3 facsimile devices.  However, many facsimile
   terminals and older versions of  TIFF-F readers are likely to not
   support the use of these higher resolutions.

   Per [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>], it is permissible for applications to treat the following
   XResolution values as being equivalent: &lt;204,200&gt; and &lt;400,408&gt;.  In
   a similar respect, the following YResolution values may also be
   treated as being equivalent: &lt;98, 100&gt;, &lt;196, 200&gt;, and &lt;391, 400&gt;.
   These equivalencies were allowed by [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>] to permit conversions
   between inch and metric based facsimile terminals.

   In a similar respect, the optional support of metric based
   resolutions in the TIFF-F reader (i.e. 77 x 38.5 cm) is included for
   completeness, since they are used in some legacy TIFF-F applications,
   but this use is not recommended for the creation of TIFF-F files by a
   writer.

<span class="h4"><a class="selflink" id="section-4.5.3" href="#section-4.5.3">4.5.3</a>. EOL byte-aligned</span>

   The historical convention for TIFF-F has been that all EOLs in
   Modified Huffman or Modified READ data must be byte-aligned. However,
   Baseline TIFF has permitted use of non-byte-aligned EOLs by default,
   so that a large percentage of TIFF-F reader implementations support



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   both conventions. Therefore, the minimum subset of TIFF-F, or Profile
   S, as defined in <a href="#section-3">Section 3</a> includes support for both byte-aligned and
   non- byte-aligned EOLs; see <a href="#section-3.2.2">Section 3.2.2</a>.

   An EOL is said to be byte-aligned when Fill bits have been added as
   necessary before EOL codes such that EOL always ends on a byte
   boundary, thus ensuring an  EOL-sequence of a one byte preceded by a
   zero nibble: xxxx0000 00000001.

   Modified Huffman encoding encodes bits, not bytes. This means that
   the end-of-line token may end in the middle of a byte. In byte
   alignment, extra zero bits (Fill) are added so that the first bit of
   data following an EOL begins on a byte boundary. In effect, byte
   alignment relieves application software of the burden of bit-
   shifting every byte while parsing scan lines for line-oriented image
   manipulation (such as writing a TIFF file).

   For Modified READ encoding, each line is terminated by an EOL and a
   one bit tag bit.  Per [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>], the value of the tag bit is 0 if the
   next line contains two dimensional data and 1 if the next line is a
   reference line.   To maintain byte alignment, fill bits are added
   before the EOL/tag bit sequence, so that the first bit of data
   following an MR tag bit begins on a byte boundary.

<span class="h4"><a class="selflink" id="section-4.5.4" href="#section-4.5.4">4.5.4</a>. EOL</span>

   As illustrated in FIGURE 1/T.4 in [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>], facsimile documents encoded
   with Modified Huffman begin with an EOL, which in TIFF-F may be byte-
   aligned. The last line of the image is not terminated by an EOL.  In
   a similar respect, images encoded with Modified READ two-dimensional
   encoding begin with an EOL, followed by a tag bit.

<span class="h4"><a class="selflink" id="section-4.5.5" href="#section-4.5.5">4.5.5</a>. RTC Exclusion</span>

   Aside from EOLs, TIFF-F files have historically only contained image
   data. This means that applications which wish to maintain strict
   conformance with the rules in [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] and compatibility with
   historical TIFF-F, SHOULD NOT include the Return To Control sequence
   (RTC) (consisting of 6 consecutive EOLs) when writing TIFF-F files.
   However, applications which need to support "transparency" of [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>]
   image data MAY include RTCs if the flag settings of the T4Options
   field are set for non-byte aligned MH or MR image data.  Implementors
   of TIFF readers should also be aware that there are some existing
   TIFF-F implementations which include the RTC sequence in MH/MR image
   data. Therefore, TIFF-F readers MUST be able to process files which
   do not include RTCs and SHOULD be able to process files which do
   include RTCs.




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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-37" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


<span class="h4"><a class="selflink" id="section-4.5.6" href="#section-4.5.6">4.5.6</a> Use of EOFB for T.6 Compressed Images</span>

   TIFF-F pages which are encoded with the T.6 Modified Modified READ
   compression method MUST include an "end-of-facsimile-block" (EOFB)
   code at the end of each coded strip. Per [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>], the EOFB code is
   followed by pad bits as needed to align on a byte boundary. TIFF
   readers SHOULD ignore any bits other than pad bits beyond the EOFB.

<span class="h3"><a class="selflink" id="section-4.6" href="#section-4.6">4.6</a>. Example Use of TIFF-F</span>

   The Profile F of TIFF (i.e. TIFF-F content) is a secondary component
   of the VPIM Message, as defined in [<a href="#ref-VPIM2" title="&quot;Voice Profile for Internet Mail - version 2&quot;">VPIM2</a>].  Voice messaging systems
   can often handle fax store-and-forward capabilities in addition to
   tradi- tional voice message store-and-forward functions.  As a
   result, TIFF-F fax messages can optionally be sent between compliant
   VPIM systems, and may be rejected if the recipient system cannot deal
   with fax.

   Refer to the VPIM Specification for proper usage of this content.

<span class="h3"><a class="selflink" id="section-4.7" href="#section-4.7">4.7</a>. Extended Black-and-white Fax Mode Summary</span>

   Recommended fields are shown with an asterisk *.

   Required fields or values are shown with a double asterisk **. If the
   double asterisk is on the field name, then all the listed values are
   required of implementations; if the double asterisks are in the
   Values column, then only the values suffixed with a double asterisk
   are required of implementations.

       +---------------------------+--------------------------------+
       | Baseline Fields           |  Values                        |
       +---------------------------+--------------------------------+
       | BitsPerSample             | 1**                            |
       +---------------------------+--------------------------------+
       | Compression               | 3**: 1D Modified Huffman and   |
       |                           |      2D Modified Read coding   |
       |                           | 4: 2D Modified Modified Read   |
       |                           |    coding                      |
       +---------------------------+--------------------------------+
       | DateTime*                 | {ASCII}: date/time in 24-hour  |
       |                           | format "YYYY:MM:DD HH:MM:SS"   |
       +---------------------------+--------------------------------+
       | FillOrder**               | 1: most significant bit first  |
       |                           | 2: least significant bit first |
       +------------------------------------------------------------+





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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


       +------------------------------------------------------------+
       | ImageDescription*         | {ASCII}: A string describing   |
       |                           | the contents of the image.     |
       +---------------------------+--------------------------------+
       | ImageWidth                | 1728**, 2048, 2432, 2592,      |
       |                           | 3072, 3456, 3648, 4096, 4864   |
       +---------------------------+--------------------------------+
       | ImageLength**             | n: total number of scanlines   |
       |                           | in image                       |
       +---------------------------+--------------------------------+
       | NewSubFileType            | 2**: Bit 1 identifies single   |
       |                           | page of a multi-page document  |
       +---------------------------+--------------------------------+
       | Orientation               | 1**-8, Default 1               |
       +---------------------------+--------------------------------+
       | PhotometricInterpretation | 0: pixel value 1 means black   |
       |  **                       | 1: pixel value 1 means white   |
       +---------------------------+--------------------------------+
       | ResolutionUnit**          | 2: inch                        |
       |                           | 3: centimeter                  |
       +---------------------------+--------------------------------+
       | RowsPerStrip**            | n: number of scanlines per     |
       |                           | TIFF strip                     |
       +---------------------------+--------------------------------+
       | SamplesPerPixel           | 1**                            |
       +---------------------------+--------------------------------+
       | Software*                 | {ASCII}: name &amp; release        |
       |                           | number of creator software     |
       +---------------------------+--------------------------------+
       | StripByteCounts**         | &lt;n&gt;: number or bytes in TIFF   |
       |                           | strip                          |
       +---------------------------+--------------------------------+
       | StripOffsets**            | &lt;n&gt;: offset from beginning of  |
       |                           | file to each TIFF strip        |
       +---------------------------+--------------------------------+
       | XResolution               | 200, 204**, 300, 400, 408      |
       |                           | (written in pixels/inch)       |
       +---------------------------+--------------------------------+
       | YResolution               | 98**, 196**, 100,              |
       |                           | 200, 300, 391, 400             |
       |                           | (written in pixels/inch)       |
       +---------------------------+--------------------------------+
       | Extension Fields                                           |
       +---------------------------+--------------------------------+







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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-39" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


       +---------------------------+--------------------------------+
       | T4Options                 | 0**: required if Compression   |
       |                           | is Modified Huffman, EOLs are  |
       |                           | not byte aligned               |
       |                           | 1: required if Compression is  |
       |                           | 2D Modified Read, EOLs are     |
       |                           | not byte aligned               |
       |                           | 4**: required if Compression   |
       |                           | is Modified Huffman, EOLs are  |
       |                           | byte aligned                   |
       +---------------------------+--------------------------------+
       | T4Options (continued)     | 5: required if Compression     |
       |                           | is 2D Modified Read, EOLs are  |
       |                           | byte aligned                   |
       +---------------------------+--------------------------------+
       | T6Options                 | 0: required if Compression is  |
       |                           | 2D Modified Modified Read      |
       +---------------------------+--------------------------------+
       | DocumentName*             | {ASCII}: name of scanned       |
       |                           | document                       |
       +---------------------------+--------------------------------+
       | PageNumber**              | n,m: page number followed by   |
       |                           | total page count               |
       +---------------------------+--------------------------------+
       | New Fields                                                 |
       +---------------------------+--------------------------------+
       | BadFaxLines*              | number of "bad" scanlines      |
       |                           | encountered during reception   |
       +---------------------------+--------------------------------+
       | CleanFaxData*             | 0: no "bad" lines              |
       |                           | 1: "bad" lines exist, but were |
       |                           | regenerated by receiver        |
       |                           | 2: "bad" lines exist, but have |
       |                           | not been regenerated           |
       +---------------------------+--------------------------------+
       | ConsecutiveBadFaxLines*   | Max number of consecutive      |
       |                           | "bad" lines received           |
       +---------------------------+--------------------------------+

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. Lossless JBIG Black-and-White Fax Mode</span>

   This section defines the lossless JBIG black-and-white mode or
   Profile J of TIFF for facsimile. Implementations of this profile are
   required to also implement Profile S.







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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   The previous section described the extended interchange set of TIFF
   fields for black-and-white fax, which provided support for the MH, MR
   and MMR compression of black-and-white images. This section adds a
   mode with JBIG compression capability.

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>. Overview</span>

   This section describes a black-and-white mode that uses JBIG
   compression. The ITU-T has approved the single-progression sequential
   mode of JBIG [<a href="#ref-T.82" title="Information technology - Coded representation of picture and audio information - Progressive bi- level image compression">T.82</a>] for Group 3 facsimile. JBIG coding offers
   improved compression for halftoned originals. JBIG compression is
   used in accordance with the application rules given in ITU-T Rec.
   T.85 [<a href="#ref-T.85" title="Application profile for Recommendation T.82 - Progressive bi-level image compression (JBIG coding scheme) for facsimile apparatus">T.85</a>].

   This mode is essentially the extended black-and-white mode with JBIG
   compression used instead of MH, MR or MMR.

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>. Required TIFF Fields</span>

   This section lists the required fields and the values they must have
   to be ITU-compatible. Besides the fields listed in <a href="#section-2.2.1">Section 2.2.1</a>, the
   extended black-and-white fax mode requires the following fields.

<span class="h4"><a class="selflink" id="section-5.2.1" href="#section-5.2.1">5.2.1</a>. Baseline fields</span>

   The TIFF fields that SHALL be used in this mode are the same as those
   described in <a href="#section-4.2.1">Section 4.2.1</a> for the extended black-and-white mode,
   with two exceptions: the following text replaces the text in <a href="#section-4.2.1">Section</a>
   <a href="#section-4.2.1">4.2.1</a> for the Compression and FillOrder fields.

Compression(259) = 9.                                              SHORT
    RequiredByTIFFBaseline
    9 = ITU-T Rec. T.82 coding, applying ITU-T Rec. T.85 (JBIG). This is
    a TIFF extension value.
    Default = 1 (and is not applicable; field must be specified).

FillOrder(266) = 2.                                            SHORT
    RequiredByTIFFBaseline
    2 = Pixels are arranged within a byte such that pixels with lower
    column values are stored in the lower-order bits of the bytes, i.e.,
    least significant bit first (LSB).

   NOTE: The JBIG coding of black-and-white image data in Profile J
   follows ITU-T Rec. T.85 [<a href="#ref-T.85" title="Application profile for Recommendation T.82 - Progressive bi-level image compression (JBIG coding scheme) for facsimile apparatus">T.85</a>], which specifies LSB first ordering
   within a byte. Note that Baseline TIFF readers are only required to
   support MSB first ordering or FillOrder = 1.

<span class="h4"><a class="selflink" id="section-5.2.2" href="#section-5.2.2">5.2.2</a>. Extension fields</span>



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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


   Same fields as those in <a href="#section-2.2.1">Section 2.2.1</a>.

<span class="h4"><a class="selflink" id="section-5.2.3" href="#section-5.2.3">5.2.3</a>. New fields</span>

   None.

<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>. Recommended TIFF Fields</span>

   See <a href="#section-2.2.3">Section 2.2.3</a> and 2.2.4.

<span class="h3"><a class="selflink" id="section-5.4" href="#section-5.4">5.4</a>.  Lossless JBIG Black-and-white Fax Mode Summary</span>

   Recommended fields are shown with an asterisk *.

   Required fields or values are shown with a double asterisk **. If the
   double asterisk is on the field name, then all the listed values are
   required of implementations; if the double asterisks are in the
   Values column, then only the values suffixed with a double asterisk
   are required of implementations.

       +---------------------------+--------------------------------+
       | Baseline Fields           |  Values                        |
       +---------------------------+--------------------------------+
       | BitsPerSample             | 1**                            |
       +---------------------------+--------------------------------+
       | Compression               | 9**: JBIG coding               |
       +---------------------------+--------------------------------+
       | DateTime*                 | {ASCII}: date/time in 24-hour  |
       |                           | format "YYYY:MM:DD HH:MM:SS"   |
       +---------------------------+--------------------------------+
       | FillOrder**               | 1: most significant bit first  |
       |                           | 2: least significant bit first |
       +---------------------------+--------------------------------+
       | ImageDescription*         | {ASCII}: A string describing   |
       |                           | the contents of the image.     |
       +---------------------------+--------------------------------+
       | ImageWidth                | 1728**, 2048, 2432, 2592,      |
       |                           | 3072, 3456, 3648, 4096, 4864   |
       +---------------------------+--------------------------------+
       | ImageLength**             | n: total number of scanlines   |
       |                           | in image                       |
       +---------------------------+--------------------------------+
       | NewSubFileType**          | 2: Bit 1 identifies single     |
       |                           | page of a multi-page document  |
       +---------------------------+--------------------------------+
       | Orientation               | 1**-8, Default 1               |
       +------------------------------------------------------------+




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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


       +---------------------------+--------------------------------+
       | PhotometricInterpretation | 0: pixel value 1 means black   |
       |  **                       | 1: pixel value 1 means white   |
       +---------------------------+--------------------------------+
       | ResolutionUnit**          | 2: inch                        |
       |                           | 3: centimeter                  |
       +---------------------------+--------------------------------+
       | RowsPerStrip**            | n: number of scanlines per     |
       |                           | TIFF strip                     |
       +---------------------------+--------------------------------+
       | SamplesPerPixel**         | 1                              |
       +---------------------------+--------------------------------+
       | Software*                 | {ASCII}: name &amp; release        |
       |                           | number of creator software     |
       +---------------------------+--------------------------------+
       | StripByteCounts**         | &lt;n&gt;: number of bytes in TIFF   |
       |                           | strip                          |
       +---------------------------+--------------------------------+
       | StripOffsets**            | &lt;n&gt;: offset from beginning of  |
       |                           | file to each TIFF strip        |
       +---------------------------+--------------------------------+
       | XResolution               | 200, 204**, 300, 400, 408      |
       |                           | (written in pixels/inch)       |
       +---------------------------+--------------------------------+
       | YResolution               | 98**, 196**, 100,              |
       |                           | 200, 300, 391, 400             |
       |                           | (written in pixels/inch)       |
       +---------------------------+--------------------------------+
       | Extension Fields                                           |
       +---------------------------+--------------------------------+
       | DocumentName*             | {ASCII}: name of document      |
       |                           |  scanned                       |
       +---------------------------+--------------------------------+
       | PageNumber**              | n,m: page number followed by   |
       |                           | total page count               |
       +---------------------------+--------------------------------+
       | New Fields                                                 |
       +---------------------------+--------------------------------+
       | GlobalParametersIFD*      | IFD: global parameters IFD     |
       +---------------------------+--------------------------------+
       | ProfileType*              | n: type of data stored in file |
       +---------------------------+--------------------------------+
       | FaxProfile*               | n: ITU-compatible fax mode     |
       +---------------------------+--------------------------------+
       | CodingMethods*            | n: compression algorithms used |
       |                           | in file                        |
       +---------------------------+--------------------------------+




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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-43" ></span>
<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. Base Color Fax Mode</span>

<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>. Overview</span>

   This section defines the lossy color mode or Profile C of TIFF for
   facsimile. Implementations of this profile are required to also
   implement Profile S.

   This is the base mode for color and grayscale facsimile, which means
   that all applications that support color fax must support this mode.
   The basic approach is the lossy JPEG compression [T.4, Annex E; T.81]
   of L*a*b* color data [<a href="#ref-T.42" title="Continuous-tone colour representation method for facsimile">T.42</a>]. Grayscale applications use the L*
   lightness component; color applications use the L*, a* and b*
   components.

   This mode uses a new PhotometricInterpretation field value to
   describe the L*a*b* encoding specified in [<a href="#ref-T.42" title="Continuous-tone colour representation method for facsimile">T.42</a>]. This encoding
   differs in two ways from the other L*a*b* encodings used in TIFF
   [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>, <a href="#ref-TTN1" title="1995">TTN1</a>]: it specifies a different default range for the a* and
   b* components, based on a comprehensive evaluation of existing
   hardcopy output, and it optionally allows selectable range for the
   L*, a* and b* components.

<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>. Required TIFF Fields</span>

   This section lists the required fields, in addition to those given in
   <a href="#section-2.2.1">Section 2.2.1</a>, and the values they must support to be compatible with
   ITU-T Rec. T.42 and Annex E in ITU-T Rec. T.4.

<span class="h4"><a class="selflink" id="section-6.2.1" href="#section-6.2.1">6.2.1</a>. Baseline Fields</span>

ImageWidth(256).                                           SHORT or LONG
    This mode supports the following fixed page widths: 864, 1024, 1216,
    1728, 2048, 2432, 2592, 3072, 3456, 3648, 4096, 4864.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

BitsPerSample(258) = 8, 12.                                        SHORT
    Count = SamplesPerPixel
    The base color fax mode requires 8 bits per sample, with 12 as an
    option. 12 bits per sample is not baseline TIFF.

Compression(259) = 7.                                              SHORT
    Base color fax mode uses Baseline JPEG compression. Value 7
    represents JPEG compression as specified in [<a href="#ref-TTN2" title="1995">TTN2</a>].



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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


FillOrder(266) = 1 , 2.                                            SHORT
    RequiredByTIFFBaseline
    Profile C readers must be able to read data in both bit orders,
    but the vast majority of facsimile products store data LSB
    first, exactly as it appears on the telephone line.
              1 = Most Significant Bit first.
              2 = Least Significant Bit first

PhotometricInterpretation(262) = 10.                               SHORT
    Base color fax mode requires pixel values to be stored using the CIE
    L*a*b* encoding defined in ITU-T Rec. T.42. This encoding is
    indicated by the PhotometricInterpretation value 10, referred to as
    ITULAB. With this encoding, the minimum sample value is  mapped to 0
    and the maximum sample value is mapped to (2^n - 1), i.e. the
    maximum value, where n is the BitsPerSample value. The conversion
    from unsigned ITULAB-encoded samples values to signed CIE L*a*b*
    values is determined by the Decode field; see Sec. 6.2.3

   NOTE: PhotometricInterpretation values 8 and 9 specify encodings for
   use with 8-bit-per-sample CIE L*a*b* [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>] and ICC L*a*b* [<a href="#ref-TTN1" title="1995">TTN1</a>]
   data, but they are fixed encodings, which use different minimum and
   maximum samples than the T.42 default encoding. As currently defined,
   they are not able to represent fax-encoded L*a*b* data.

ResolutionUnit(296) = 2, 3.                                        SHORT
    The unit of measure for resolution. 2 = inch, 3 = centimeter;
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277) = 1, 3.                                       SHORT
    1: L* component only, required in base color mode
    3: L*, a*, b* components
    Encoded according to PhotometricInterpretation field

XResolution(282) = 100, 200, 300, 400.                          RATIONAL
YResolution(283) = 100, 200, 300, 400.                          RATIONAL
    The resolution of the image is expressed in pixels per resolution
    unit. In pixels per inch, allowed XResolution values are: 100, 200,
    300, and 400. The base color fax mode requires the pixels to be
    square, hence YResolution must equal XResolution. Base resolution is
    200 pixels per inch and SHALL be supported by all implementations of
    this mode. See <a href="#section-2.2.2">Section 2.2.2</a> for inch-metric equivalency.

NOTE: Not all combinations of XResolution, YResolution and ImageWidth
are legal. The following table gives the legal combinations for inch-
based resolutions and the corresponding paper sizes [<a href="#ref-T.30">T.30</a>].






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    +--------------------------------+---------------------------+
    |   XResolution x YResolution    |         ImageWidth        |
    +--------------------------------+---------------------------+
    |           100 x 100            |   864   |  1024  |  1216  |
    +--------------------------------+---------------------------+
    |           200 x 200            |  1728   |  2048  |  2432  |
    +--------------------------------+---------------------------+
    |           300 x 300            |  2592   |  3072  |  3648  |
    +--------------------------------+---------------------------+
    |           400 x 400            |  3456   |  4096  |  4864  |
    +--------------------------------+---------------------------+
                                     |Letter,A4|   B4   |   A3   |
                                     |  Legal  |        |        |
                                     +---------------------------+
                                     |         Paper Size        |
                                     +---------------------------+

<span class="h4"><a class="selflink" id="section-6.2.2" href="#section-6.2.2">6.2.2</a> Extension Fields</span>

The JPEG compression standard allows for the a*b* chroma components of
an image to be subsampled relative to the L* lightness component. The
extension fields ChromaSubSampling and ChromaPositioning define the
subsampling. They are the same as YCbCrSubSampling and YCbCrPositioning
in [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>], but have been renamed to reflect their applicability to other
color spaces.

ChromaSubSampling(530).                                            SHORT
    Count = 2
    Specifies the subsampling factors for the chroma components of a
    L*a*b* image. The two subfields of this field, ChromaSubsampleHoriz
    and ChromaSubsampleVert, specify the horizontal and vertical
    subsampling factors respectively.

    SHORT 0: ChromaSubsampleHoriz = 1, 2.
    1: equal numbers of lightness and chroma samples horizontally,
    2: twice as many lightness samples as chroma samples horizontally,

    SHORT 1: ChromaSubsampleVert = 1, 2.
    1: equal numbers of lightness and chroma samples vertically,
    2: twice as many lightness samples as chroma samples vertically,

    The default value for ChromaSubSampling is (2,2), which is the
    default for chroma subsampling in color fax [T.4, Annex E]. No
    chroma subsampling, i.e. ChromaSubSampling = (1,1), is an option
    for color fax

ChromaPositioning(531) = 1.                                        SHORT
    Specifies the spatial positioning of chroma components relative to



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    the lightness component.
    1: centered,
    A value of 1 means chrominance samples are spatially offset and
    centered with respect to luminance samples. See the current TIFF
    specification under YcbCr positioning for further information.
    Default = 1, which is what ITU-T T.4, Annex E specifies.

<span class="h4"><a class="selflink" id="section-6.2.3" href="#section-6.2.3">6.2.3</a>. New Fields</span>

Decode(433).                                                   SRATIONAL
    Count = 2 * SamplesPerPixel
    Describes how to map image sample values into the range of values
    appropriate for the current color space. In general, the values are
    taken in pairs and specify the minimum and maximum output value for
    each color component. For the base color fax mode, Decode has a
    count of 6 values and maps the unsigned ITULAB-encoded sample values
    (Lsample, asample, bsample) to signed L*a*b* values, as follows:.

        L* = Decode[0] + Lsample x (Decode[1]-Decode[0])/(2^n -1)
        a* = Decode[2] + asample x (Decode[3]-Decode[2])/(2^n -1)
        b* = Decode[4] + bsample x (Decode[5]-Decode[4])/(2^n -1)

    where Decode[0], Decode[2] and Decode[4] are the minimum values for
    L*, a* and b*; Decode[1], Decode[3] and Decode[5] are the maximum
    values for L*, a* and b*; and n is the BitsPerSample, either 8 or
    12. For example, when n=8, L*=Decode[0] when Lsample=0 and
    L*=Decode[1] when Lsample=255.

    ITU-T Rec. T.42 specifies the ITULAB encoding in terms of a range
    and offset for each component, which are related to the minimum and
    maximum values as follows:

        minimum = - (range x offset) / 2^n - 1
        maximum = minimum + range

    The Decode field default values depend on the color space. For the
    ITULAB color space encoding, the default values correspond to the
    base range and offset, as specified in ITU-T Rec. T.42 [<a href="#ref-T.42" title="Continuous-tone colour representation method for facsimile">T.42</a>]. The
    following table gives the base range and offset values for
    BitsPerSample=8 and 12, and the corresponding default minimum and
    maximum default values for the Decode field, calculated using the
    equations above when PhotometricInterpetation=10.









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                       +-----------------------------------------------+
                       | ITU-T Rec. T.42  |           Decode           |
 +---------+-----------|   base values    |       default values       |
 | BitsPer + Component +------------------+----------------------------+
 | -Sample |           |  Range | Offset  |      Min     |     Max     |
 +---------+-----------+--------+---------+--------------+-------------+
 |    8    |    L*     |   100  |    0    |       0      |     100     |
 |         +-----------+--------+---------+--------------+-------------+
 |         |    a*     |   170  |   128   |  -21760/255  |  21590/255  |
 |         +-----------+--------+---------+--------------+-------------+
 |         |    b*     |   200  |    96   |  -19200/255  |  31800/255  |
 +---------+-----------+--------+---------+--------------+-------------+
 |   12    |    L*     |   100  |    0    |       0      |     100     |
 |         +-----------+--------+---------+--------------+-------------+
 |         |    a*     |   170  |  2048   | -348160/4095 | 347990/4095 |
 |         +-----------+--------+---------+--------------+-------------+
 |         |    b*     |   200  |  1536   | -307200/4095 | 511800/4095 |
 +---------+-----------+--------+---------+--------------+-------------+

   For example, when PhotometricInterpretation=10 and BitsPerSample=8,
   the default value for Decode is (0, 100, -21760/255, 21590/255,
   -19200/255, 31800/255).

<span class="h3"><a class="selflink" id="section-6.3" href="#section-6.3">6.3</a>. Recommended TIFF Fields</span>

   See Sections <a href="#section-2.2.3">2.2.3</a>. and 2.2.4.

<span class="h3"><a class="selflink" id="section-6.4" href="#section-6.4">6.4</a> Base Color Fax Mode Summary</span>

   Recommended fields are shown with an asterisk *

   Required fields or values are shown with a double asterisk **. If the
   double asterisk is on the field name, then all the listed values are
   required of implementations; if the double asterisks are in the
   Values column, then only the values suffixed with a double asterisk
   are required of implementations.

       +---------------------------+--------------------------------+
       | Baseline Fields           | Values                         |
       +---------------------------+--------------------------------+
       | BitsPerSample             | 8**: 8 bits per color sample   |
       |                           | 12: optional 12 bits/sample    |
       +---------------------------+--------------------------------+
       | Compression**             | 7: JPEG                        |
       +---------------------------+--------------------------------+
       | DateTime*                 | {ASCII}: date/time in 24-hour  |
       |                           | format "YYYY:MM:DD HH:MM:SS"   |
       +---------------------------+--------------------------------+



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       +------------------------------------------------------------+
       | FillOrder**               | 1: most significant bit first  |
       |                           | 2: least significant bit first |
       +---------------------------+--------------------------------+
       | ImageDescription*         | {ASCII}: A string describing   |
       |                           | the contents of the image.     |
       +---------------------------+--------------------------------+
       | ImageWidth                | 864, 1024, 1216, 1728**, 2048  |
       |                           | 2432, 2592, 3072, 3456, 3648   |
       |                           | 4096, 4864                     |
       +---------------------------+--------------------------------+
       | ImageLength**             | n: total number of scanlines   |
       |                           | in image                       |
       +---------------------------+--------------------------------+
       | NewSubFileType**          | 2: Bit 1 identifies single page|
       |                           | of a multi-page document       |
       +---------------------------+--------------------------------+
       | Orientation               | 1**-8, Default 1               |
       +---------------------------+--------------------------------+
       | PhotometricInterpretation | 10**: ITULAB                   |
       +---------------------------+--------------------------------+
       | ResolutionUnit**          | 2: inch                        |
       |                           | 3: centimeter                  |
       +---------------------------+--------------------------------+
       | RowsPerStrip**            | n: number of scanlines per     |
       |                           | TIFF strip                     |
       +---------------------------+--------------------------------+
       | SamplesPerPixel           | 1**: L* (lightness)            |
       |                           | 3: LAB                         |
       +---------------------------+--------------------------------+
       | Software*                 | {ASCII}: name &amp; release number |
       |                           | of creator software            |
       +---------------------------+--------------------------------+
       | StripByteCounts**         | &lt;n&gt;: number or bytes in        |
       |                           | TIFF strip                     |
       +---------------------------+--------------------------------+
       | StripOffsets**            | &lt;n&gt;: offset from beginning     |
       |                           | of file to each TIFF strip     |
       +---------------------------+--------------------------------+
       | XResolution               | 100, 200**, 300, 400 (written  |
       |                           | in pixels/inch)                |
       +---------------------------+--------------------------------+
       | YResolution               | 100, 200**, 300, 400           |
       |                           | (must equal XResolution)       |
       +---------------------------+--------------------------------+






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       +---------------------------+--------------------------------+
       | Extension Fields                                           |
       +---------------------------+--------------------------------+
       | DocumentName*             | {ASCII}: name of scanned       |
       |                           | document                       |
       +---------------------------+--------------------------------+
       | PageNumber**              | n,m: page number followed by   |
       |                           | total page count               |
       +---------------------------+--------------------------------+
       | ChromaSubSampling         | (1,1), (2, 2)**                |
       |                           | (1, 1): equal numbers of       |
       |                           | lightness and chroma samples   |
       |                           | horizontally and vertically    |
       |                           | (2, 2): twice as many lightness|
       |                           | samples as chroma samples      |
       |                           | horizontally and vertically    |
       +---------------------------+--------------------------------+
       | ChromaPositioning         | 1**: centered                  |
       +---------------------------+--------------------------------+
       | New Fields                                                 |
       +---------------------------+--------------------------------+
       | Decode**                  | minL, maxL, mina, maxa, minb,  |
       |                           | maxb: minimum and maximum      |
       |                           | values for L*a*b*              |
       +---------------------------+--------------------------------+
       | GlobalParametersIFD*      | IFD: IFD containing            |
       |                           | global parameters              |
       +---------------------------+--------------------------------+
       | ProfileType*              | n: type of data stored in      |
       |                           | TIFF file                      |
       +---------------------------+--------------------------------+
       | FaxProfile*               | n: ITU-compatible fax mode     |
       +---------------------------+--------------------------------+
       | CodingMethods*            | n: compression algorithms      |
       |                           | used in file                   |
       +---------------------------+--------------------------------+
       | VersionYear*              | byte sequence: year of ITU std |
       +---------------------------+--------------------------------+

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Lossless Color Mode</span>

   This section defines the lossless color mode or Profile L of TIFF for
   facsimile. Implementations of this profile are required to also
   implement Profiles S and C.







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<span class="h3"><a class="selflink" id="section-7.1" href="#section-7.1">7.1</a>. Overview</span>

   This mode, defined in [<a href="#ref-T.43" title="Colour and gray-scale image representations using lossless coding scheme for facsimile">T.43</a>], uses JBIG to losslessly code three
   types of color and grayscale images: one bit per color CMY, CMYK and
   RGB images; a palettized (i.e. mapped) color image; and continuous
   tone color and grayscale images. The last two are multi-level and use
   the L*a*b* encoding specified in [<a href="#ref-T.42" title="Continuous-tone colour representation method for facsimile">T.42</a>].

<span class="h4"><a class="selflink" id="section-7.1.1" href="#section-7.1.1">7.1.1</a>. Color Encoding</span>

   While under development, this mode was called T.Palette, as one of
   its major additions was palette or mapped color images. Baseline TIFF
   only allows RGB color maps, but ITU-T Rec. T.43 requires L*a*b* color
   maps, using the encoding specified in ITU-T Rec. T.42. Palette color
   images are expressed with indices (bits per sample) of 12 bits or
   less, or optionally 13 to 16 bits, per [<a href="#ref-T.43" title="Colour and gray-scale image representations using lossless coding scheme for facsimile">T.43</a>].

   Enabling T.43 color maps in TIFF requires the extension field
   Indexed, defined in [<a href="#ref-TTN1" title="1995">TTN1</a>], and the PhotometricInterpretation field
   value 10, defined in <a href="#section-6.2.1">Section 6.2.1</a>. The following table shows the
   corresponding PhotometricInterpretation, SamplesPerPixel,
   BitsPerSample and Indexed field values for the different T.43 image
   types.

       +----------------------------------------------------------+
       | Image Type |PhotometricIn| Samples  | Bits Per | Indexed |
       |            |-terpretation| PerPixel |  Sample  |         |
       |------------+-------------+----------+----------+---------|
       |     RGB    |    2=RGB    |     3    |    1     |    0    |
       +----------------------------------------------------------+
       |     CMY    |    5=CMYK   |     3    |    1     |    0    |
       +------------+-------------+----------+----------+---------+
       |     CMYK   |    5=CMYK   |     4    |    1     |    0    |
       +------------+-------------+----------+----------+---------+
       |   Palette  |  10=ITULAB  |     1    |    n     |    1    |
       +------------+-------------+----------+----------+---------+
       |  Grayscale |  10=ITULAB  |     1    |   8, 12  |    0    |
       +------------+-------------+----------+----------+---------+
       |    Color   |  10=ITULAB  |     3    |   8, 12  |    0    |
       +------------+-------------+----------+----------+---------+

<span class="h4"><a class="selflink" id="section-7.1.2" href="#section-7.1.2">7.1.2</a>. JBIG Encoding</span>

   T.43 uses the single-progression sequential mode of JBIG, defined in
   ITU-T Rec. T.82. To code multi-level images using JBIG, which is a
   bi-level compression method, an image is resolved into a set of bit-
   planes, and each bit-plane is then JBIG compressed. For continuous
   tone color and grayscale images, Gray code conversion is used. The



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   Gray code conversion is part of the data stream encoding, and is
   therefore invisible to TIFF.

<span class="h3"><a class="selflink" id="section-7.2" href="#section-7.2">7.2</a>. Required TIFF Fields</span>

   This section lists the required fields, in addition to those in
   <a href="#section-2.2.1">Section 2.2.1</a>, and the values they must have to be compatible with
   ITU-T Rec. T.43.

<span class="h4"><a class="selflink" id="section-7.2.1" href="#section-7.2.1">7.2.1</a>. Baseline Fields</span>

ImageWidth(256).                                           SHORT or LONG
    Same page widths as the base color mode; see <a href="#section-6.2.1">Section 6.2.1</a>.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

BitsPerSample(258) = 1, 2-8, 9-16.                                 SHORT
    Count = SamplesPerPixel
    RGB, CMY, CMYK: 1 bit per sample
    Continuous tone (L*a*b*): 2-8 bits per sample, 9-12 bits optional
    Palette color: 12 or fewer bits per sample, 13-16 bits optional
    Note: More than 8 bits per sample is not baseline TIFF.

ColorMap(320).                                                     SHORT
    Count = 3 * number of sample values
    Lossless color fax mode supports palette-color (indexed) images
    where the single component value is used as an index into a full
    color lookup table stored in the ColorMap field. The sample value is
    encoded using the number of bits given by the BitsPerSample field
    value. However, per [<a href="#ref-T.43" title="Colour and gray-scale image representations using lossless coding scheme for facsimile">T.43</a>],the number of sample values may be less
    than 2**BitsPerSample. The color lookup table is only required to
    have as many entries as there are number of sample values. For
    palette-color images in lossless color fax mode, the ITULAB encoding
    with 8 or optionally 12 bits per color map value is supported. To
    utilize a color map, the TIFF Indexed field must be present. TIFF
    orders the color map values so that all the L* values come first,
    followed by all the a* values and then all the b* values. Because
    ITU-T Rec. T.43 specifies a "chunky" ordering with the L*a*b*
    components of the first value, followed by those of the second
    value, and so on, reproducing color map values from a fax data
    stream in a TIFF file requires reordering values.

Compression(259) = 10.                                             SHORT
10: ITU-T Rec. T.43 representation, using ITU-T Rec. T.82 (JBIG)
    coding



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FillOrder(266) = 1 , 2.                                            SHORT
    RequiredByTIFFBaseline
    Profile F readers must be able to read data in both bit orders,
    but the vast majority of facsimile products store data LSB
    first, exactly as it appears on the telephone line.
              1 = Most Significant Bit first.
              2 = Least Significant Bit first

PhotometricInterpretation(262) = 2, 5, 10.                         SHORT
    2: RGB
    5: CMYK, including CMY
    10: ITULAB
    Image data may also be stored as palette color images, where pixel
    values are represented by a single component that is an index into a
    color map using the ITULAB encoding. This color map is specified by
    the ColorMap field. To use palette color images, set the
    PhotometricInterpretation to 10,SamplesPerPixel to 1, and Indexed to
    1. The color map is stored in the ColorMap field. See <a href="#section-7.1.1">Section 7.1.1</a>
    for further discussion on the color encoding.

ResolutionUnit(296) = 2, 3.                                        SHORT
    The unit of measure for resolution. 2 = inch, 3 = centimeter;
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277) = 1, 3, 4.                                    SHORT
    1: Palette color image, or L*-only if Indexed = 0 and
       PhotometricInterpretation is 10 (ITULAB).
    3: RGB, or L*a*b*, or CMY if PhotometricInterpretation is 5 (CMYK).
    4: CMYK.

XResolution(282) = 100, 200, 300, 400.                          RATIONAL
YResolution(283) = 100, 200, 300, 400.                          RATIONAL
    The resolution of the image is expressed in pixels per resolution
    unit. In pixels per inch, allowed XResolution values are: 100, 200,
    300, and 400. The lossless color fax mode requires the pixels to be
    square, hence YResolution must equal XResolution. Base resolution is
    200 pixels per inch. See <a href="#section-2.2.2">Section 2.2.2</a> for inch-metric equivalency.

<span class="h4"><a class="selflink" id="section-7.2.2" href="#section-7.2.2">7.2.2</a>. Extension Fields</span>

Indexed(364) = 0, 1.                                               SHORT
    0: not a palette-color image
    1: palette-color image
    This field is used to indicate that each sample value is an index
    into an array of color values specified in the ColorMap field.
    Lossless color fax mode supports palette-color images with the
    ITULAB encoding. The SamplesPerPixel value must be 1.




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<span class="h4"><a class="selflink" id="section-7.2.3" href="#section-7.2.3">7.2.3</a>. New Fields</span>

Decode(433)                                                    SRATIONAL
    Decode is used in connection with the ITULAB encoding of image data
    and color map values; see <a href="#section-6.2.3">Section 6.2.3</a>.

<span class="h3"><a class="selflink" id="section-7.3" href="#section-7.3">7.3</a>. Recommended TIFF Fields</span>

   See Sections <a href="#section-2.2.3">2.2.3</a>. and 2.2.4.

<span class="h3"><a class="selflink" id="section-7.4" href="#section-7.4">7.4</a>. Lossless Color Fax Mode Summary</span>

   Recommended fields are shown with an asterisk *.

        +--------------------+--------------------------------------+
        |   Baseline Fields  |             Values                   |
        +--------------------+--------------------------------------+
        | BitsPerSample      | 1: Binary RGB, CMY(K)                |
        |                    | 8: 8 bits per color sample           |
        |                    | 9-16: optional                       |
        +--------------------+--------------------------------------+
        | ColorMap           | n: LAB color map                     |
        +--------------------+--------------------------------------+
        | Compression        | 10: JBIG, per T.43                   |
        +--------------------+--------------------------------------+
        | DateTime*          | {ASCII}:  date/time in the 24-hour   |
        |                    | format "YYYY:MM:DD HH:MM:SS"         |
        +--------------------+--------------------------------------+
        | FillOrder**        | 1: Most significant bit first        |
        |                    | 2: Least significant bit first       |
        +--------------------+--------------------------------------+
        | ImageDescription*  | {ASCII}: A string describing the     |
        |                    | contents of the image.               |
        +--------------------+--------------------------------------+
        | ImageWidth         | 864, 1024, 1216, 1728**, 2048, 2432, |
        |                    | 2592, 3072, 3456, 3648, 4096, 4864   |
        +--------------------+--------------------------------------+
        | ImageLength**      | n: total number of scanlines in image|
        +--------------------+--------------------------------------+
        | NewSubFileType     | 2: Bit 1 identifies single page of a |
        |                    | multi-page document                  |
        +--------------------+--------------------------------------+
        | Orientation        | 1**-8, Default 1                     |
        +--------------------+--------------------------------------+
        | PhotometricInter-  | 2: RGB                               |
        | pretation          | 5: CMYK                              |
        |                    | 10: ITULAB                           |
        +--------------------+--------------------------------------+



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        +--------------------+--------------------------------------+
        | ResolutionUnit     | 2: inch                              |
        |                    | 3: centimeter                        |
        +--------------------+--------------------------------------+
        | RowsPerStrip       | n: number of scanlines per TIFF strip|
        +--------------------+--------------------------------------+
        | SamplesPerPixel    | 1: L* (lightness)                    |
        |                    | 3: LAB, RGB, CMY                     |
        |                    | 4: CMYK                              |
        +--------------------+--------------------------------------+
        | Software*          | {ASCII}: name &amp; release number of    |
        |                    | creator software                     |
        +--------------------+--------------------------------------+
        | StripByteCounts    | &lt;n&gt;: number or bytes in TIFF strip   |
        +--------------------+--------------------------------------+
        | StripOffsets       | &lt;n&gt;: offset from beginning of file to|
        |                    | each TIFF strip                      |
        +--------------------+--------------------------------------+
        | XResolution        | 100, 200, 300, 400 (written in       |
        |                    | pixels/inch)                         |
        +--------------------+--------------------------------------+
        | YResolution        | equal to XResolution (pixels must be |
        |                    | square)                              |
        +--------------------+--------------------------------------+
        | Extension Fields                                          |
        +--------------------+--------------------------------------+
        | DocumentName*      | {ASCII}: name of scanned document    |
        +--------------------+--------------------------------------+
        | PageNumber         | n,m: page number followed by total   |
        |                    | page count                           |
        +--------------------+--------------------------------------+
        | Indexed            | 0: not a palette-color image         |
        |                    | 1: palette-color image               |
        +--------------------+--------------------------------------+
        | New Fields                                                |
        +--------------------+--------------------------------------|
        | Decode             | minL, maxL, mina, maxa, minb, maxb:  |
        |                    |minimum and maximum values for L*a*b* |
        +--------------------+--------------------------------------+
        | GlobalParameters   | IFD: global parameters IFD           |
        | IFD*               |                                      |
        +-----------------------------------------------------------+









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        +--------------------+--------------------------------------+
        | ProfileType*       | n: type of data stored in TIFF file  |
        +--------------------+--------------------------------------+
        | FaxProfile*        | n: ITU-compatible fax mode           |
        +--------------------+--------------------------------------+
        | CodingMethods*     | n:compression algorithms used in     |
        |                    | file                                 |
        +--------------------+--------------------------------------+
        | VersionYear*       | byte sequence: year of ITU fax std   |
        +--------------------+--------------------------------------+

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Mixed Raster Content Mode</span>

   This section defines the Mixed Raster Content mode or Profile M of
   TIFF for facsimile. Implementations of this profile are required to
   implement Profiles S and C, and may optionally implement Profiles F,
   J and L.

<span class="h3"><a class="selflink" id="section-8.1" href="#section-8.1">8.1</a>. Overview</span>

   Unlike previous fax modes, which use a single coding method and
   spatial resolution for an entire fax page, the Mixed Raster Content
   mode [<a href="#ref-T.44" title="Mixed Raster Content (MRC)">T.44</a>] enables different coding methods and resolutions within a
   single page. For example, consider a page that contains black-and-
   white text, which is best coded with MMR or JBIG, a color bar chart,
   best coded with JBIG, and a scanned color image, best coded with
   JPEG. Similarly, while spatial resolution of 400 pixels per inch may
   be best for the black-and- white text, 200 pixel per inch is usually
   sufficient for a color image.

   Rather than applying one coding method and resolution to all
   elements, MRC allows multiple coders and resolutions within a page.
   By itself, MRC does not define any new coding methods or resolutions.
   Instead it defines a 3-layer image model for structuring and
   combining the scanned image data. The MRC 3-layer model has been
   applied here using the TIFF format to yield a data structure which
   differs from [<a href="#ref-T.44" title="Mixed Raster Content (MRC)">T.44</a>] though it applies the same coding methods, uses
   the same compressed image data stream and is consistent with the TIFF
   principle of a single IFD per image.

<span class="h4"><a class="selflink" id="section-8.1.1" href="#section-8.1.1">8.1.1</a>. MRC 3-layer model</span>

   The 3 layers of the MRC model are Foreground and Background, which
   are both multi-level, and Mask, which is bi-level. Each layer may
   appear only once on a page and is coded independently of the other
   two. In our earlier example, the black-and-white text could be in the
   Mask layer, the color chart in the Foreground layer, and the color
   image in the Background layer.



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   Each layer is an image and, when present, is represented by at least
   one IFD in a TIFF file. This is consistent with TIFF, which provides
   fields to define the attributes, such as resolution, image size, bits
   per sample, etc., of a single image or layer. The distribution of
   content among layers is determined by the writer, as is the choice of
   coding method, color encoding and spatial resolution for a layer.

   The final image is obtained by using the Mask layer to select pixels
   from the other two layers. When the Mask layer pixel value is 1, the
   corresponding pixel from the Foreground layer is selected; when it is
   0, the corresponding pixel from the Background layer is selected.
   Details are given in the Introduction of [<a href="#ref-T.44" title="Mixed Raster Content (MRC)">T.44</a>].

   Not all pages, and not all parts of a page, require 3 layers. If
   there is only one layer present, then that layer is the primary image
   or IFD. If there is more than one layer, then the Mask must be one of
   the layers, in which case it is the primary image and it must be page
   size.

   MRC allows a page to be split into strips, with a variable number of
   scanlines in a strip. A strip can have 1, 2 or 3 layers. A single,
   stripped layer may be stored as a single, stripped image in an IFD,
   e.g., all strips associated with the Background layer may be treated
   as a single image. Alternatively, each strip associated with a layer
   may be stored as a separate image or IFD, e.g., the Background layer
   can be composed of several images that are offset vertically with
   respect to the page. In this case, there can be no overlap between
   images associated with a single layer. According to [<a href="#ref-T.4" title="Standardization of group 3 facsimile apparatus for document transmission">T.4</a>] Annex G,
   strips having more than 1 layer SHOULD NOT be more than 256 lines in
   length unless the capability to receive longer strips has been
   negotiated.

   Furthermore, color fax also requires the spatial resolutions of
   Background and Foreground images to be legal fax values that are also
   integer factors of the Mask image resolution. For example, if the
   Mask Layer resolution is 400 pixels per inch, then allowed
   resolutions for the Foreground and Background layers are 100, 200 or
   400 pixels per inch; if the Mask is at 300 pixels per inch, then
   allowed values are 100 and 300. The Foreground and Background layer
   resolutions can be independently set.

<span class="h4"><a class="selflink" id="section-8.1.2" href="#section-8.1.2">8.1.2</a>. A TIFF Representation for the MRC 3-layer model</span>

   In the TIFF representation of the 3-layer MRC model, each page is
   represented by a single IFD, called the Primary IFD, that represents
   the Mask layer (unless the Foreground or Background is the single
   layer present), and a set of child IFDs that are referenced through
   the SubIFDs extension field [<a href="#ref-TTN1" title="1995">TTN1</a>]. To distinguish MRC-specific



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   SubIFDs from other SubIFDs, the NewSubFileType field MUST have Bit 4
   ON, indicating an MRC-related IFD. A new ImageLayer field is also
   introduced that consists of two values that identify the layer
   (Foreground, Background, or Mask) and the order within the layer
   (first, second, ... image of the layer); see <a href="#section-8.2.3">Section 8.2.3</a>.

   Because MRC allows strips with variable numbers of scanlines, a
   reader MUST support StripRowCounts field because a writer may use it
   in place of the RowsPerStrip field in this mode. The StripRowCounts
   field allows each layer, with a variable number of scanlines in each
   strip, to be represented by a single IFD, when the coding parameters
   are the same for all strips in the layer. The MRC standard [<a href="#ref-T.44" title="Mixed Raster Content (MRC)">T.44</a>]
   allows the Foreground and Background layers to have strips with
   different coding parameters. In this case, a separate IFD is required
   to represent the strips which use different coding parameters; see
   text in next paragraph. In all cases, the Mask layer is required to
   be represented by a single IFD and a single set of coding parameters.

   The use of SubIFDs to store child IFDs is described in [<a href="#ref-TTN1" title="1995">TTN1</a>]. An
   example is shown graphically below. The Primary IFD associated with
   page 1 (PrimaryIFD 0) points to page 2 (PrimaryIFD 1) with the
   nextIFD offset. The Primary IFD, corresponding to the Mask layer
   (ImageLayer=[2,1]), contains a SubIFDs field that points to a list of
   child IFDs. The first child IFD represents one image of the
   Background layer, i.e., ImageLayer=[1,1]. This child IFD points to
   the second child IFD via the nextIFD offset. This child represents
   the second Background layer image, ImageLayer=[1,2]. Finally, the
   second child points to the third child, which corresponds to the
   single Foreground layer image, ImageLayer=[3,1]. The next IFD offset
   associated with this Foreground image is 0, indicating no more child
   IFDs exist. Each primary IFD has the NewSubFileType set to 18,
   indicating the IFD is MRC-specific (bit 4) and that it is a single
   page of a multi-page document (bit 1). Each child IFD has the
   NewSubFileType set to 16, indicating the IFD is MRC-specific. The 'V'
   character should be read as a down-pointing arrow.

                       (nextIFD)
       PRIMARY IFD 0  ------------&gt; PRIMARY IFD 1--&gt; ...
           ImageLayer = [2,1]
           NewSubFileType = 18
           SubIFDs
                |
                V
             Child IFD
                ImageLayer = [1,1]
                NewSubFileType = 16
                |
                |(nextIFD)



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                |
                V
             Child IFD
                ImageLayer = [1,2]
                NewSubFileType = 16
                |
                |(nextIFD)
                |
                V
             Child IFD
                ImageLayer = [3,1]
                NewSubFileType = 16
                |
                |(nextIFD)
                V
                0

   In the example above, the SubIFDs field of the Primary IFD points to
   the first IFD in a list of child IFDs. TIFF allows the SubIFDs field
   to point to an array of IFDs, each of which can be the first of a
   list of IFDs. An MRC-enabled TIFF reader must scan all available
   child IFDs to locate and identify IFDs associated with MRC layers.

   In the case where the Background or Foreground layers are described
   with multiple IFDs, the XPosition and YPosition TIFF fields specify
   the offset to the upper-left corner of the IFD with respect to the
   Mask layer; see <a href="#section-8.2.2">Section 8.2.2</a>. When there is only a single layer
   (Mask, Foreground, or Background), it is stored as the Primary IFD.

<span class="h3"><a class="selflink" id="section-8.2" href="#section-8.2">8.2</a>. Required TIFF Fields</span>

   This section describes the TIFF fields required, in addition to those
   in <a href="#section-2.2.1">Section 2.2.1</a>, to represent MRC mode fax images. Since MRC mode
   stores fax data as a collection of images corresponding to layers or
   parts of layers, the coding methods, color encodings and spatial
   resolutions used by previous modes apply to MRC. Therefore, the
   descriptions here will typically reference the appropriate earlier
   section. Fields and values specific to MRC mode are pointed out.

<span class="h4"><a class="selflink" id="section-8.2.1" href="#section-8.2.1">8.2.1</a>. Baseline Fields</span>

ImageWidth(256).                                           SHORT or LONG
    Same page widths as the base color mode; see <a href="#section-6.2.1">Section 6.2.1</a>.
    In the MRC mode, the width of a Foreground or Background image in
    the coded data stream may be less than the page width. In this case,
    the image width in the coded data steam is used to interpret the
    coded data, and the value of this field is used as the page width.




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NewSubFileType(254) = 16, 18.                                       LONG
    For MRC fax mode, the NewSubFileType field has two bits that are
    required.
    Bit 1 indicates a single page of a multi-page document and must be
    set for the Primary IFD;
    Bit 4 indicates MRC imaging model as described in ITU-T
    Recommendation T.44 [<a href="#ref-T.44" title="Mixed Raster Content (MRC)">T.44</a>], and must be set for Primary IFDs
    and all MRC-specific child IFDs.

BitsPerSample(258) = 1, 2-8, 9-16                                  SHORT
Compression(259) = 3, 4, 7, 9, 10.                                 SHORT
SamplesPerPixel(277) = 1, 3, 4.                                    SHORT

FillOrder(266) = 1 , 2.                                            SHORT
    RequiredByTIFFBaseline
    Profile F readers must be able to read data in both bit orders,
    but the vast majority of facsimile products store data LSB
    first, exactly as it appears on the telephone line.
              1 = Most Significant Bit first.
              2 = Least Significant Bit first

ResolutionUnit(296) = 2, 3.                                        SHORT
PhotometricInterpretation(262) = 0, 1, 2, 5, 10.                   SHORT
    For Mask layer, see Sections <a href="#section-4.2.1">4.2.1</a> and <a href="#section-5.2.1">5.2.1</a>.
    For Foreground and Background layers, see Sections <a href="#section-6.2.1">6.2.1</a> and <a href="#section-7.2.1">7.2.1</a>.

ColorMap(320).                                                     SHORT
Count = 3 * (2**BitsPerSample)
    Used when Foreground or Background layer is a palette-color image;
    see <a href="#section-7.2.1">Section 7.2.1</a>.

XResolution(282) = 100, 200, 300, 400.                          RATIONAL
YResolution(283) = 100, 200, 300, 400.                          RATIONAL
    The resolution of the image is expressed in pixels per resolution
    unit. In pixels per inch, allowed XResolution values for all layers
    are: 100, 200, 300, and 400. MRC color fax mode requires the pixels
    to be square, hence YResolution must equal XResolution for all
    layers. The resolution of Background and Foreground layers must each
    be an integer factor of the Primary image, which is the Mask layer,
    when it is present; see <a href="#section-8.4">Section 8.4</a>.
    See <a href="#section-2.2.2">Section 2.2.2</a> for inch-metric equivalency.

<span class="h4"><a class="selflink" id="section-8.2.2" href="#section-8.2.2">8.2.2</a>. Extension Fields</span>

ChromaSubSampling(530).                                            SHORT
ChromaPositioning(531).                                            SHORT
    For Foreground and Background layers, see <a href="#section-6.2.2">Section 6.2.2</a>.




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Indexed(346) = 0, 1.                                               SHORT
    For Foreground and Background layers: 1 indicates a palette-color
    image, see <a href="#section-7.2.2">Section 7.2.2</a>.

T4Options(292) = 0, 1, 4, 5.                                       SHORT
T6Options(293) = 0.                                                SHORT
    For Mask layer, see <a href="#section-4.2.2">Section 4.2.2</a>.

SubIFDs(330).                                                        IFD
    Count = number of child IFDs
    Each value is an offset from the beginning of the TIFF file to a
    child IFD [<a href="#ref-TTN1" title="1995">TTN1</a>].

XPosition(286).                                                 RATIONAL
YPosition(287).                                                 RATIONAL
    Specifies the horizontal and vertical offsets of the top-left of the
    IFD from the top-left of the Primary IFD in page resolution units.
    For example, if the Primary IFD is at 400 pixels per inch, and a
    foreground layer IFD is at 200 pixels per inch and located at pixel
    coordinate (345, 678) with respect to the Primary IFD, the XPosition
    value is 345/400 and the YPosition value is 678/400.
    Color fax does not currently allow overlap of any component images
    within a single layer.
    Default values for XPosition and YPosition are 0.

<span class="h4"><a class="selflink" id="section-8.2.3" href="#section-8.2.3">8.2.3</a>. New Fields</span>

Decode(433).                                                   SRATIONAL
    For Foreground and Background layers, see <a href="#section-6.2.3">Section 6.2.3</a>.

DefaultImageColor(434).                                            SHORT
    Count = SamplesPerPixel
    In areas where no image data is available, a default color is needed
    to specify the color value. If the StripByteCounts value for a strip
    is 0, then the color for that strip must be defined by a default
    image color.

    The DefaultImageColor field uses the same encoding as the image
    data, and its value is therefore interpreted using the
    PhotometricInterpretation, SamplesPerPixel, BitsPerSample, and
    Indexed fields. If the fax data stream requires a different
    encoding, then transferring the default color value between a TIFF
    file and fax data stream requires a color conversion.
    For the Foreground layer image, the default value for the
    DefaultImageColor field is black. For other cases, including the
    Background layer image, the default value is white.





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StripRowCounts(559).                                                LONG
    Count = number of strips
    The number of scanlines stored in a strip. MRC allows each fax strip
    to store a different number of scanlines. For strips with more than
    one layer there is a maximum strip size of 256 scanlines or full
    page size. The 256 maximum SHOULD be used unless the capability to
    receive longer strips has been negotiated. This field replaces
    RowsPerStrip for IFDs with variable-sized strips. Only one of the
    two fields, StripRowCounts and RowsPerStrip, may be used in an IFD.

ImageLayer (34732).                                       SHORT or LONG.
    Count = 2
    Image layers are defined such that layer 1 is the Background layer,
    layer 3 is the Foreground layer, and layer 2 is the Mask layer,
    which selects pixels from the Background and Foreground layers. The
    ImageLayer tag contains two values, describing the layer to which
    the image belongs and the order in which it is imaged.

    ImageLayer[0] = 1, 2, 3.
    1: Image is a Background image, i.e., the image that will appear
       whenever the Mask contains a value of 0. Background images
       typically contain low-resolution, continuous-tone imagery.
    2: Image is the Mask layer. In MRC, if the Mask layer is present, it
       must be the Primary IFD and be full page in extent (no gaps.)
    3: Image is a Foreground image, i.e., the image that will appear
       whenever the Mask contains a value of 1. The Foreground image
       generally defines the color of text or lines, but may also
       contain high-resolution imagery.

    ImageLayer[1]:
    1: first image to be imaged in this layer,
    2: second image to be imaged in this layer,
    3: ...

    Value describing the image order. In MRC, this may be considered
    the strip number. Since MRC mode currently does not allow overlap
    between images within a layer, the order value does not have any
    visual effect.

   In MRC fax mode, it is possible that only a single layer is
   transmitted. For example, if a page contains only a single
   continuous-tone photograph, then only the Background layer may be
   transmitted. In this case, the Background layer will be stored as the
   Primary IFD. ImageLayer[0] will be 1 indicating Background;
   ImageLayer[1] will be 1 since there can be no other IFDs associated
   with that layer. No Mask layer will exist.





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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


<span class="h3"><a class="selflink" id="section-8.3" href="#section-8.3">8.3</a>. Recommended TIFF Fields</span>

   See Sections <a href="#section-2.2.3">2.2.3</a>. and 2.2.4.

<span class="h3"><a class="selflink" id="section-8.4" href="#section-8.4">8.4</a>. Rules and Requirements for Images</span>

   The MRC mode defines a fundamental set of rules for images in the 3-
   layer representation.

   1. If more than one layer exists, then the binary Mask layer SHALL be
      present and be the primary image. The Mask layer SHALL support the
      encoding defined in <a href="#section-3">Section 3</a> and MAY support the encodings
      defined in Sections <a href="#section-4">4</a> and <a href="#section-5">5</a>. If only one layer exists, then the
      image corresponding to that layer is the primary image.

   2. When the binary Mask layer is the Primary IFD, the Primary IFD
      defines and extends to the entire page boundary; all attached
      model images cannot extend beyond the Primary image. Resolution
      differences may cause some pixels to "hang over" the page
      boundary, but no new pixels should exist completely beyond the
      page extent. When the Foreground or Background layer is the
      Primary IFD, the Primary IFD may not be page width.

   3. The Background and Foreground images SHALL support the color
      encoding defined in <a href="#section-6">Section 6</a> and MAY support the color encoding
      defined in <a href="#section-7">Section 7</a>. These images MAY optionally cover only a
      portion of the strip or page.

   4. Each Primary IFD and each MRC-specific SubIFD must have an
      ImageLayer field to specify which layer the IFD belongs to, and
      the imaging order of that IFD within the layer.

   5. Each Primary IFD must have a NewSubFileType field value set to 18,
      indicating a single page of a multi-page document (bit 1) and MRC
      mode (bit 4).

   6. Each MRC-specific child IFD must have a NewSubFileType field value
      set to 16, indicating MRC mode (bit 4).

   7. In MRC mode, each layer is transmitted as a sequence of strips. It
      is possible that each strip of each layer can be stored as a
      separate IFD. In this case, the SubIFDs structure pointed to by
      the Primary IFD will contain several IFDs that have an ImageLayer
      field with the layer identified as either Background (layer 1) or
      Foreground (layer 3). There may be no overlap in the vertical
      direction between IFDs associated with a single layer, although





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      there may be a gap from one of these images to the next. The TIFF
      XPosition and YPosition fields are used to indicate the placement
      of these images with respect to the primary image.

   8. When the Mask image is present, the resolution of Background and
      Foreground images must each be an integer factor of the Mask
      image. For example, if the Mask image is 400 pixels/inch, then the
      Background or Foreground image may be at 400 pixels/inch (400/1),
      200 pixels/inch (400/2) or 100 pixels/inch (400/4).

<span class="h3"><a class="selflink" id="section-8.5" href="#section-8.5">8.5</a>. MRC Fax Mode Summary</span>

   Recommended fields are shown with an asterisk *

       +------------------+-----------------------------------------+
       | Baseline Fields  |               Values                    |
       |------------------|-----------------------------------------|
       | BitsPerSample    | 1: binary mask                          |
       |                  | 8: 8 bits per color sample              |
       |                  | 9-16: optional 12 bits/sample           |
       +------------------+-----------------------------------------+
       | ColorMap         | n: LAB color map                        |
       +------------------+-----------------------------------------+
       | Compression      | 3: Modified Huffman and Modified Read   |
       |                  | 4: Modified Modified Read               |
       |                  | 7: JPEG                                 |
       |                  | 9: JBIG, per T.85                       |
       |                  | 10: JBIG, per T.43                      |
       +------------------+-----------------------------------------+
       | DateTime*        | {ASCII): date/time in the 24-hour format|
       |                  | "YYYY:MM:DD HH:MM:SS"                   |
       +------------------+-----------------------------------------|
       | FillOrder**      | 1: Most significant bit first           |
       |                  | 2: Least significant bit first          |
       +------------------+-----------------------------------------|
       | ImageDescription*| {ASCII}: A string describing the        |
       |                  | contents of the image.                  |
       +------------------+-----------------------------------------+
       | ImageWidth       | 864, 1024, 1216, 1728**, 2048, 2432,    |
       |                  | 2592, 3072, 3456, 3648, 4096, 4864      |
       +------------------+-----------------------------------------+
       | ImageLength**    | n: total number of scanlines in image   |
       +------------------+-----------------------------------------+
       | NewSubFileType   | 16, 18:                                 |
       |                  | Bit 1 indicates single page of a multi- |
       |                  | page document on Primary IFD            |
       |                  | Bit 4 indicates MRC model               |
       +------------------+-----------------------------------------+



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       +------------------+-----------------------------------------+
       | Orientation      | 1**-8, Default 1                        |
       +------------------+-----------------------------------------+
       | PhotometricInter | 0: WhiteIsZero                          |
       | pretation        | 1: BlackIsZero                          |
       |                  | 2: RGB                                  |
       |                  | 5: CMYK                                 |
       |                  | 10: ITULAB                              |
       +------------------+-----------------------------------------+
       | ResolutionUnit   | 2: inch                                 |
       |                  | 3: centimeter                           |
       +------------------+-----------------------------------------+
       | RowsPerStrip     | n: number or scanlines per strip        |
       +------------------+-----------------------------------------+
       | SamplesPerPixel  | 1: L* (lightness)                       |
       |                  | 3: RGB, LAB, CMY                        |
       |                  | 4: CMYK                                 |
       +------------------+-----------------------------------------+
       | Software*        | {ASCII}: name &amp; release number of       |
       |                  | creator software                        |
       +------------------+-----------------------------------------+
       | StripByteCounts  | &lt;n&gt;: number or bytes in each strip      |
       +------------------+-----------------------------------------+
       | StripOffsets     | &lt;n&gt;: offset from beginning of file to   |
       |                  | each TIFF strip                         |
       +------------------+-----------------------------------------|
       | XResolution      | 100, 200, 300, 400 (written in          |
       |                  | pixels/inch)                            |
       +------------------+-----------------------------------------|
       | YResolution      | equal to XResolution (pixels must be    |
       |                  | square)                                 |
       +------------------+-----------------------------------------+
       | Extension Fields                                           |
       +------------------+-----------------------------------------+
       | T4Options        | 0: required if Compression is Modified  |
       |                  | Huffman, EOLs not byte aligned          |
       |                  | 1: required if Compression 2D Modified  |
       |                  | Read, EOLs are not byte aligned         |
       |                  | 4: required if Compression Modified     |
       |                  | Huffman, EOLs byte aligned              |
       |                  | 5: required if Compression 2D Modified  |
       |                  | Read, EOLs are byte aligned             |
       +------------------+-----------------------------------------+
       | T6Options        | 0: required if Compression is 2D        |
       |                  | Modified Modified Read                  |
       +------------------+-----------------------------------------+





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       +------------------+-----------------------------------------+
       | DocumentName*    | {ASCII}: name of scanned document       |
       +------------------+-----------------------------------------+
       | PageNumber       | n,m: page number followed by total page |
       |                  | count                                   |
       +------------------+-----------------------------------------+
       | ChromaSubSampling| (1,1), (2, 2)**                         |
       |                  | (1, 1): equal numbers of lightness and  |
       |                  | chroma samples horizontally &amp; vertically|
       |                  | (2, 2): twice as many lightness samples |
       |                  | as chroma horizontally and vertically   |
       +------------------+-----------------------------------------+
       | ChromaPositioning| 1: centered                             |
       +------------------+-----------------------------------------+
       | Indexed          | 0: not a palette-color image            |
       |                  | 1: palette-color image                  |
       +------------------+-----------------------------------------+
       | SubIFDs          | &lt;IFD&gt;: byte offset to fg/bg IFDs        |
       +------------------+-----------------------------------------+
       | XPosition        | horizontal offset in primary IFD        |
       |                  | resolution units                        |
       +------------------+-----------------------------------------+
       | YPosition        | vertical offset in primary IFD          |
       |                  | resolution units                        |
       +------------------+-----------------------------------------+
       | New Fields                                                 |
       +------------------+-----------------------------------------+
       | Decode           | minL, maxL, mina, maxa, minb, maxb:     |
       |                  | minimum and maximum values for L*a*b*   |
       +------------------+-----------------------------------------+
       | DefaultImageColor| &lt;n&gt;: background color                   |
       +------------------+-----------------------------------------+
       | StripRowCounts   | &lt;n&gt;: number of scanlines in each strip  |
       +------------------+-----------------------------------------+
       | ImageLayer       | n, m: layer number, imaging sequence    |
       |                  | (e.g., strip number)                    |
       +------------------+-----------------------------------------+
       | GlobalParameters | IFD: global parameters IFD              |
       | IFD*             |                                         |
       +------------------+-----------------------------------------+
       | ProfileType*     | n: type of data stored in TIFF file     |
       +------------------+-----------------------------------------+
       | FaxProfile*      | n: ITU-compatible fax mode              |
       +------------------+-----------------------------------------+
       | CodingMethods*   | n: compression algorithms used in file  |
       +------------------+-----------------------------------------+
       | ModeNumber*      | n: version of ITU fax standard          |
       +------------------+-----------------------------------------+



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       +------------------------------------------------------------+
       | VersionYear*     | byte sequence: year of ITU fax standard |
       +------------------+-----------------------------------------+

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. MIME content-type image/tiff</span>

   [<a id="ref-TIFF-REG">TIFF-REG</a>] describes the registration of the MIME content-type
   image/tiff to refer to TIFF encoded image data. When transported by
   MIME, the TIFF content defined by this document must be encoded
   within an image/tiff content type. In addition, an optional
   "application" parameter is defined for image/tiff to identify a
   particular application's subset of TIFF and TIFF extensions for the
   encoded image data, if it is known. Typically, this would be used to
   assist the recipient in dispatching a suitable rendering package to
   handle the display or processing of the image file.

<span class="h3"><a class="selflink" id="section-9.1" href="#section-9.1">9.1</a> Refinement of MIME content-type image/tiff for Facsimile</span>
<span class="h3">   Applications</span>

   Since this document defines facsimile specific profiles of TIFF, it
   is useful to note an appropriate application parameter for the
   image/tiff MIME content-type.

   The two values of the image/tiff application parameter as defined for
   facsimile are shown below, separated by a comma:

       faxbw, faxcolor

   The "faxbw" application parameter is suitable for use by applications
   that can process one or more TIFF for facsimile profiles or subsets
   used for the encoding of black and white facsimile data.

   The "faxcolor" application parameter is suitable for use by
   applications that can process one or more TIFF for facsimile profiles
   or subsets that can be used for the encoding of black and white, AND
   color facsimile data.

   Since this document defines several profiles of TIFF for facsimile,
   the following rules should be followed when setting the application
   parameter value. For TIFF image data which is encoded for the
   profiles of TIFF for Facsimile that support black-and-white image
   data (Profiles S, F or J), applications which use one of these
   profiles or a subset should set the value of the application
   parameter to "faxbw". For TIFF image data which is encoded for the
   defined profiles of TIFF for Facsimile that support color image data
   (Profiles C, L or M), as well as black-and-white image data,
   applications which use one of these profiles or a subset should set
   the value of the application parameter to "faxcolor".



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   An example of the use of the image/tiff MIME Content-type with the
   application parameter set with the value 'faxbw' follows:

       Content-type: image/tiff; application=faxbw

   In this example, use of this parameter value will enable applications
   to identify the content as being within a profile or subset of TIFF
   for Facsimile that is suitable for encoding black and white image
   data, Before attempting to process the image data.

   In a similar respect, an example of the image/tiff MIME Content-type
   with the application parameter setting suitable for handling a color
   subset or profile of TIFF for facsimile is shown below:

       Content-type: image/tiff; application=faxcolor

<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. Security Considerations</span>

   This document describes a file format for Internet fax, which is a
   series of profiles of TIFF for facsimile. As such, it does not create
   any security issues not already identified in [<a href="#ref-TIFF-REG" title="&quot;Tag Image File Format (TIFF) - image/tiff MIME Sub-type Registration&quot;">TIFF-REG</a>], in its use
   of fields as defined in [<a href="#ref-TIFF" title="Revision 6.0">TIFF</a>].  There are also new TIFF fields
   defined within this specification, but they are of a purely
   descriptive nature, so that no new security risks are incurred.

   Further, the encoding specified in this document does not in any way
   preclude the use of any Internet security protocol to encrypt,
   authenticate, or non-repudiate TIFF-encoded facsimile messages.

<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>. References</span>

   [<a id="ref-REQ">REQ</a>] Bradner, S, "Key words for use in RFCs to Indicate Requirement
   Levels", <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-T.4">T.4</a>] ITU-T Recommendation T.4, Standardization of group 3 facsimile
   apparatus for document transmission, October 1997

   [<a id="ref-T.6">T.6</a>] ITU-T Recommendation T.6, Facsimile coding schemes and coding
   control functions for group 4 facsimile apparatus, November 1988

   [<a id="ref-T.30">T.30</a>] ITU-T Recommendation T.30 - Procedures for Document Facsimile
   Transmission in the General Switched Telephone Network, June 1996

   [<a id="ref-T.42">T.42</a>] ITU-T Recommendation T.42, Continuous-tone colour
   representation method for facsimile, February 1996






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   [<a id="ref-T.43">T.43</a>] ITU-T Recommendation T.43, Colour and gray-scale image
   representations using lossless coding scheme for facsimile, February
   1997

   [<a id="ref-T.44">T.44</a>] ITU-T Recommendation T.44, Mixed Raster Content (MRC), October
   1997.

   [<a id="ref-T.81">T.81</a>] ITU-T Recommendation T.81, Information technology - Digital
   compression and coding of continuous-tone still images - Requirements
   and guidelines, September 1992

   [<a id="ref-T.82">T.82</a>] ITU-T Recommendation T.82, Information technology - Coded
   representation of picture and audio information - Progressive bi-
   level image compression, March 1995

   [<a id="ref-T.85">T.85</a>] ITU-T Recommendation T.85, Application profile for
   Recommendation T.82 - Progressive bi-level image compression (JBIG
   coding scheme) for facsimile apparatus, August 1995

   [<a id="ref-TIFF">TIFF</a>] Tag Image File Format, Revision 6.0, Adobe Developers
   Association, June 3, 1992,
   <a href="ftp://ftp.adobe.com/pub/adobe/devrelations/devtechnotes/pdffiles/tiff6.pdf">ftp://ftp.adobe.com/pub/adobe/devrelations/</a>
   <a href="ftp://ftp.adobe.com/pub/adobe/devrelations/devtechnotes/pdffiles/tiff6.pdf">devtechnotes/pdffiles/tiff6.pdf</a>

        The TIFF 6.0 specification dated June 3, 1992 specification (c)
        1986-1988, 1992 Adobe Systems Incorporated. All Rights Reserved.

   [<a id="ref-TIFF-FY">TIFF-FY</a>] Parsons, G.  and J. Rafferty, "Tag Image File Format (TIFF)
   - F Profile for Facsimile", <a href="./rfc2306">RFC 2306</a>, March 1998.

   [<a id="ref-TIFF-F0">TIFF-F0</a>] TIFF Class F specification, Apr 28, 1990,
   <a href="ftp://ftp.faximum.com/pub/documents/tiff_f.txt">ftp://ftp.faximum.com/pub/documents/tiff_f.txt</a>

   [<a id="ref-TIFF-REG">TIFF-REG</a>] Parsons, G., Rafferty J. and S. Zilles, "Tag Image File
   Format (TIFF) - image/tiff MIME Sub-type Registration",  <a href="./rfc2302">RFC 2302</a>,
   March 1998.

   [<a id="ref-TTN1">TTN1</a>] Adobe PageMaker 6.0 TIFF Technical Notes, Sept. 14, 1995,
   <a href="http://www.adobe.com/supportservice/devrelations/PDFS/TN/TIFFPM6.pdf">http://www.adobe.com/supportservice/devrelations/PDFS/TN/TIFFPM6.pdf</a>

   [<a id="ref-TTN2">TTN2</a>] Draft TIFF Technical Note 2, Replacement TIFF/JPEG
   specification, March 17, 1995,
   <a href="ftp://ftp.sgi.com/graphics/tiff/TTN2.draft.txt">ftp://ftp.sgi.com/graphics/tiff/TTN2.draft.txt</a>

   [<a id="ref-VPIM2">VPIM2</a>] Vaudreui,l G. and G. Parsons, "Voice Profile for Internet
   Mail - version 2", work in progress, &lt;<a href="./draft-ema-vpim-06.txt">draft-ema-vpim-06.txt</a>&gt;

   The ITU-T Recommendations are available at <a href="http://www.itu.ch">http://www.itu.ch</a>.



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<span class="h2"><a class="selflink" id="section-12" href="#section-12">12</a>. Authors' Addresses</span>

   Lloyd McIntyre                     Stephen Zilles
   Xerox Corporation                  Adobe Systems Inc.
   Mailstop PAHV-305                  Mailstop W14
   3400 Hillview Ave.                 345 Park Avenue
   Palo Alto, CA 94304 USA            San Jose, CA 95110-2704, USA
   Voice: +1-650-813-6762             Voice: +1-408-536-4766
   Fax: +1-650-845-2340               Fax: +1-408-536-4042
   Email: lmcintyre@adoc.xerox.com    Email: szilles@adobe.com

   Robert Buckley                     Dennis Venable
   Xerox Corporation                  Xerox Corporation
   Mailstop 0128-30E                  Mailstop 0128-27E
   800 Phillips Road                  800 Phillips Road
   Webster, NY 14580, USA             Webster, NY 14580, USA
   Voice: +1-716-422-1282             Voice: +1-716-422-8009
   Fax: +1-716-422-6117               Fax: +1-716-422-6117
   Email: Rob_Buckley@wb.xerox.com    Email: venable@wrc.xerox.com

   Glenn S. Parsons                   James Rafferty
   Northern Telecom                   Human Communications
   P.O. Box 3511, Station C           12 Kevin Drive
   Ottawa, ON  K1Y 4H7, Canada        Danbury, CT 06811-2901, USA
   Phone: +1-613-763-7582             Phone: +1-203-746-4367
   Fax: +1-613-763-2697               Fax: +1-203-746-4367
   Email: Glenn.Parsons@Nortel.ca     Email: Jrafferty@worldnet.att.net
























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<span class="grey"><a href="./rfc2301">RFC 2301</a>              File Format for Internet Fax            March 1998</span>


Annex A:  Summary of TIFF Fields for Internet Fax

   This annex includes tables which list by mode the TIFF fields used in
   the proposed fax file format.  The fields are organized into 3
   categories:

      1)  TIFF Baseline Fields
      2)  TIFF Extension Fields
      3)  New Fields.

   The tables include the allowed values for each fax mode. Entries
   other than explicit numbers are described by:

      n        - single number
      n, m     - 2 numbers
      a, b, c  - 3 numbers
      r        - rational number
      &lt;n&gt;      - array of numbers
      &lt;b&gt;      - byte sequence
      {ASCII}  - string
      IFD      - IFD byte offset
      &lt;IFD&gt;    - array of IFD byte offsets

   A blank entry in the table indicates that the field is not used by
   that particular fax mode.

Table A.1  TIFF Baseline Fields

            +---------------------------------------------------------+
            |                    Fax Mode/Profile                     |
            +---------------------------------------------------------|
            | Minimal | Extended |  JBIG  |  Lossy  |Lossless| Mixed  |
 +----------|   B&amp;W   |    B&amp;W   |  B&amp;W   |  Color  | Color  | Raster |
 |   TIFF   |         |          |        |         |        | Content|
 |  Field   |    S    |     F    |   J    |    C    |   L    |   M    |
 +----------+---------+----------+--------+---------+--------+--------+
 | BitsPer  | 1       | 1        | 1      | 8, 12   | 1, 2-8 | 1, 2-8 |
 | Sample   |         |          |        |         | 9-16   | 9-16   |
 +----------+---------+----------+--------+---------+--------+--------+
 | ColorMap |         |          |        |         | &lt;n&gt;    | &lt;n&gt;    |
 +----------+---------+----------+--------+---------+--------+--------+
 | Compres- | 3       | 3, 4     | 9      | 7       | 10     | 3, 4, 7|
 | sion     |         |          |        |         |        | 9,10   |
 +----------+---------+----------+--------+---------+--------+--------+
 | DateTime |         | {ASCII}  | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
 +----------+---------+----------+--------+---------+--------+--------+
 | FillOrder| 2       | 1, 2     | 1, 2   | 1, 2    | 1, 2   | 1,2    |
 +----------+---------+----------+--------+---------+--------+--------+



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 +----------+---------+----------+--------+---------+--------+--------+
 | ImageDes-|         | {ASCII}  | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
 | cription |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Image-   | n       | n        | n      | n       | n      | n      |
 | Length   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Image-   | 1728    | 1728, 2048, 2432  |   864, 1024, 1216, 1728,  |
 | Width    |         | 2592, 3072, 3456  |  2048, 2432, 2592, 3072,  |
 |          |         | 3648, 4096, 4864  |  3456, 3648, 4096, 4864   |
 +----------+---------+----------+--------+---------+--------+--------+
 | NewSub-  | 2       | 2        | 2      | 2       | 2      | 16, 18 |
 | FileType |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Orien-   | 1       | 1-8      | 1-8    | 1-8     | 1-8    | 1-8    |
 | tation   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Photo-   | 0       | 0, 1     | 0, 1   | 10      | 2, 5,  | 0, 1,  |
 | metric-  |         |          |        |         | 10     | 2, 5,  |
 | Interp-  |         |          |        |         |        | 10     |
 | retation |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Resolu-  | 2       | 2, 3     | 2, 3   | 2, 3    | 2, 3   | 2, 3   |
 | tionUnit |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | RowsPer- | n       | n        | n      | n       | n      | n      |
 | Strip    |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Samples- | 1       | 1        | 1      | 1, 3    | 1, 3, 4| 1, 3, 4|
 | PerPixel |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Software |         | {ASCII}  | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
 +----------+---------+----------+--------+---------+--------+--------+
 | Strip-   | n       | &lt;n&gt;      | &lt;n&gt;    | &lt;n&gt;     | &lt;n&gt;    | &lt;n&gt;    |
 | Byte-    |         |          |        |         |        |        |
 | Counts   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Strip-   | n       | &lt;n&gt;      | &lt;n&gt;    | &lt;n&gt;     | &lt;n&gt;    | &lt;n&gt;    |
 | Offsets  |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | XResolu- | 204     | 200, 204, 300     |    100, 200, 300, 400     |
 | tion     | 200     | 400, 408          |                           |
 +----------+---------+----------+--------+---------+--------+--------+
 | YResolu- | 98, 196 | 98, 196, 100, 200 |    100, 200, 300, 400     |
 | tion     | 100,200 | 300, 391, 400     |                           |
 +----------+---------+----------+--------+---------+--------+--------+





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Table A.2  TIFF Extension Fields

            +---------------------------------------------------------+
            |                    Fax Mode/Profile                     |
            +---------------------------------------------------------|
            | Minimal | Extended |  JBIG  |  Lossy  |Lossless| Mixed  |
 +----------|   B&amp;W   |    B&amp;W   |  B&amp;W   |  Color  | Color  | Raster |
 |   TIFF   |         |          |        |         |        | Content|
 |  Field   |    S    |     F    |   J    |    C    |   L    |   M    |
 +----------+---------+----------+--------+---------+--------+--------+
 | Chroma-  |         |          |        | 1       |        | 1      |
 | Position-|         |          |        |         |        |        |
 | ing      |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Chroma-  |         |          |        | &lt;1, 1&gt;  |        | &lt;1, 1&gt; |
 | SubSampl-|         |          |        | &lt;2, 2&gt;  |        | &lt;2, 2&gt; |
 | ing      |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Document-|         | {ASCII}  | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
 | Name     |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Indexed  |         |          |        |         | 0,1    | 0,1    |
 +----------+---------+----------+--------+---------+--------+--------+
 | Page-    | n, m    | n, m     | n, m   | n, m    | n, m   | n, m   |
 | Number   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | SubIFDs  |         |          |        |         |        | &lt;IFD&gt;  |
 +----------+---------+----------+--------+---------+--------+--------+
 | T4Options| 0, 4    | 0, 1,    |        |         |        | 0, 1,  |
 |          |         | 4, 5     |        |         |        | 4, 5   |
 +----------+---------+----------+--------+---------+--------+--------+
 | T6Options|         | 0        |        |         |        | 0      |
 +----------+---------+----------+--------+---------+--------+--------+
 | XPosition|         |          |        |         |        | r      |
 +----------+---------+----------+--------+---------+--------+--------+
 | YPosition|         |          |        |         |        | r      |
 +----------+---------+----------+--------+---------+--------+--------+














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Table A.3   New Fields

            +---------------------------------------------------------+
            |                    Fax Mode/Profile                     |
            +---------------------------------------------------------|
            | Minimal | Extended |  JBIG  |  Lossy  |Lossless| Mixed  |
 +----------|   B&amp;W   |    B&amp;W   |  B&amp;W   |  Color  | Color  | Raster |
 |   TIFF   |         |          |        |         |        | Content|
 |  Field   |    S    |     F    |   J    |    C    |   L    |   M    |
 +----------+---------+----------+--------+---------+--------+--------+
 | BadFax-  |         | n        |        |         |        |        |
 | Lines    |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | CleanFax-|         | 0, 1, 2  |        |         |        |        |
 | Data     |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Coding-  |         |          | n      | n       | n      | n      |
 | Method   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Consecu- |         | n        |        |         |        |        |
 | tiveBad- |         |          |        |         |        |        |
 | FaxLines |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Decode   |         |          |        | &lt;r&gt;     | &lt;r&gt;    | &lt;r&gt;    |
 +----------+---------+----------+--------+---------+--------+--------+
 | Default- |         |          |        |         |        | &lt;n&gt;    |
 |ImageColor|         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Fax-     |         |          | n      | n       | n      | n      |
 | Profile  |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Global-  |         | IFD      | IFD    | IFD     | IFD    | IFD    |
 | Parame-  |         |          |        |         |        |        |
 | tersIFD  |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Image-   |         |          |        |         |        | n, m   |
 | Layer    |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Mode-    |         |          |        |         |        | n      |
 | Number   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------|
 | Profile- |         |          | n      | n       | n      | n      |
 | Type     |         |          |        |         |        |        |
 +--------------------------------------------------------------------+







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 +----------+---------+----------+--------+---------+--------+--------+
 | Strip-   |         |          |        |         |        | &lt;n&gt;    |
 | RowCounts|         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Version- |         |          |        | &lt;b&gt;     |&lt;b&gt;     |        |
 | Year     |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+












































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Annex B.  IANA Registration for image/tiff Application Parameter
Values used for facsimile

   To: IANA@isi.edu

   Subject: Registration of new Application parameter values for
   image/tiff

   MIME media type name: image/tiff

   Optional parameters: Application

   New Value(s): faxbw, faxcolor

   Description of Use:

   faxbw - The "faxbw" application parameter is suitable for use by
   applications that can process one or more TIFF for facsimile profiles
   or subsets used for the encoding of black-and-white facsimile data.
   The definition of the use of this value is contained in <a href="#section-9">Section 9</a> of
   this document (TIFFPLUS).

   Faxcolor - The "faxcolor" application parameter is suitable for use
   by applications that can process one or more TIFF for facsimile
   profiles or subsets that can be used for the encoding of black and
   white, AND color facsimile data. The definition of the use of this
   value is contained in <a href="#section-9">Section 9</a> of this document (TIFFPLUS).
























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Security Considerations:

   Security considerations related to use of the TIFF subsets described
   by the "faxbw" and "faxcolor" values of the Application parameter are
   identified in <a href="#section-10">Section 10</a> of this document (TIFFPLUS).

Persons &amp; email addresses to contact for further information:

   Glenn W. Parsons (Glenn.Parsons@Nortel.ca)
   James Rafferty (Jrafferty@worldnet.att.net)
   Stephen Zilles (szilles@adobe.com)

   Change Controller:  Stephen Zilles

INFORMATION TO THE SUBMITTER:

   The accepted registrations will be listed in the "Assigned Numbers"
   series of RFCs.  The information in the registration form is freely
   distributable.
































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Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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</pre>