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<!ENTITY email         "esr@thyrsus.com">
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<article><title>Introduction to GIFLIB</title>

<articleinfo>

<author>
  <firstname>Eric</firstname>
  <othername>Steven</othername>
  <surname>Raymond</surname>
  <affiliation>
    <orgname><ulink url="&homepage;">
    Thyrsus Enterprises</ulink></orgname> 
    <address>
    <email>&email;</email>
    </address>
  </affiliation>
</author>
<copyright>
  <year>2012</year>
  <holder role="mailto:&email;">Eric S. Raymond</holder> 
</copyright>

</articleinfo>

<para>GIFLIB is a package of portable tools and library routines for
working with GIF images.</para>

<para>The Graphics Interchange Format(c) specification is the copyrighted
property of CompuServe Incorporated.  GIF(sm) is a service mark
property of CompuServe Incorporated.</para>

<para>This package has been released under an X Consortium-like open-source
license.  Use and copy as you see fit.  If you make useful changes,
add new tools, or find and fix bugs, please send your mods to the
maintainers for general distribution.</para>

<para>The util directory includes programs to clip, rotate, scale, and
position GIF images.  These are no replacement for an interactive graphics
editor, but they can be very useful for scripted image generation or
transformation.</para>

<para>The library includes program-callable entry points for reading and writing
GIF files, an 8x8 utility font for embedding text in GIFs, and an error
handler.  GIF manipulation can be done at a relatively low level by
sequential I/O (which automatically does/undoes image compression) or at
a higher level by slurping an entire GIF into allocated core.</para>

<para>This library speaks both GIF87a and GIF89.  The differences
between GIF87 and GIF89 are minor: in the latter, the interpretation
of some extension block types is defined.  The library never needs to
actually interpret these, but <ulink
url="giftext.html">giftext</ulink> notices them and there are
functions in the API to read and modify them.</para>

<sect1><title>Utilities</title>

<para>Here is a summary of the utilities in this package.  If you're looking
at this page through a web browser, each utility name should be a
hotlink to HTML documentation.</para>

<para>Most utilities have a -v (verbose) option that will cause them to print
the current input scan line number (counting up) whenever they read
image input, and will print output image line number (counting down)
when they dump output.  Utilities that only read or write always print
in increasing order.</para>

<!--
Note: the giflib.1 man page is deliberately omitted from the following
list of references. It's meant to be seen through man(1) only as part
of a local installation of the tools.
-->

<sect2><title>Conversion Utilities</title>

<variablelist>
<varlistentry>
<term><ulink url="gif2rgb.html">gif2rgb</ulink></term>
<listitem>
<para>convert images saved as GIF to 24-bit RGB image(s) or vice-versa</para>
</listitem>
</varlistentry>
</variablelist>

</sect2>
<sect2><title>Image Manipulation Components</title>

<variablelist>
<varlistentry>
<term><ulink url="gifclrmp.html">gifclrmp</ulink></term>
<listitem>
<para>modify GIF image colormaps</para>
</listitem>
</varlistentry>
<varlistentry>
<term><ulink url="giffix.html">giffix</ulink></term>
<listitem>
<para>clumsily attempts to fix truncated GIF images</para>
</listitem>
</varlistentry>
</variablelist>

</sect2>
<sect2><title>Report Generators</title>

<variablelist>
<varlistentry>
<term><ulink url="giftext.html">giftext</ulink></term>
<listitem>
<para>print (text only) general information about a GIF</para>
</listitem>
</varlistentry>
</variablelist>

</sect2>
<sect2><title>GIF Composition Tools</title>

<variablelist>
<varlistentry>
<term><ulink url="gifbuild.html">gifbuild</ulink></term>
<listitem>
<para>converter/deconverter to/from an editable text format</para>
</listitem>
</varlistentry>
<varlistentry>
<term><ulink url="giftool.html">giftool</ulink></term>
<listitem>
<para>GIF transformation tool</para>
</listitem>
</varlistentry>
</variablelist>

</sect2>
<sect2><title>Obsolete utilities</title>

<para>These are used for testing by the GFLIB developers and no longer
installed by a normal build.</para>

<variablelist>
<varlistentry>
<term><ulink url="gifbg.html">gifbg</ulink></term>
<listitem>
<para>generate a single-color test pattern GIF</para>
</listitem>
</varlistentry>
<varlistentry>
<term><ulink url="gifcolor.html">gifcolor</ulink></term>
<listitem>
<para>generate color test patterns</para>
</listitem>
</varlistentry>
<varlistentry>
<term><ulink url="gifwedge.html">gifwedge</ulink></term>
<listitem>
<para>create a test GIF image resembling a color monitor test pattern</para>
</listitem>
</varlistentry>
<varlistentry>
<term><ulink url="gifhisto.html">gifhisto</ulink></term>
<listitem>
<para>generate color-frequency histogram from a GIF</para>
</listitem>
</varlistentry>
<varlistentry>
<term><ulink url="gifecho.html">gifecho</ulink></term>
<listitem>
<para>generate GIF images out of regular text in 8x8 font</para>
</listitem>
</varlistentry>
<varlistentry>
<term><ulink url="gifinto.html">gifinto</ulink></term>
<listitem>
<para>end-of-pipe fitting for GIF-processing pipelines</para>
</listitem>
</varlistentry>
</variablelist>


</sect2>
</sect1>
<sect1><title>Library Functions</title>

<para>The library contains two groups of C functions.  One group does
sequential I/O on the stream-oriented GIF format.  The other supports
grabbing an entire GIF into allocated core, operating on it in core,
and then writing the modified in-core GIF out to disk.</para>

<para>Unless you are on extremely memory-limited machine, you probably want
to use the second group.</para>

<para>Detailed documentation on the library entry points is in <ulink
url="gif_lib.html">gif_lib.html</ulink>.</para>

</sect1>
<sect1><title>The GIF Standard</title>

<para>The doc subdirectory includes an <ulink
url="gifstandard/GIF89a.html">HTML presentation of the GIF
standard</ulink>; an <ulink url="gifstandard/
LZW-and-GIF-explained.html">explanation of Lempel-Ziv
compression</ulink>, and the original flat-ASCII description of <ulink
url="gifstandard/gif89.txt">GIF89 format</ulink> . For historical
completeness, we also include a copy of the <ulink
url="gifstandard/gif87.txt">GIF87 standard.</ulink></para>

<para>You can also read a <ulink url="whatsinagif/index.html">
detailed narrative description</ulink> of how GIFs are laid out.  It
clarifies some points on which the standard is obscure.</para>

</sect1>
<sect1><title>Package Status</title>

<para>GIFLIB's current maintainer is Eric S. Raymond.  You can find his home
page at <ulink url="&homepage;">&homepage;</ulink>.</para>

<para>GIFLIB is not under active development, but bug fixes are being
accepted.</para>

</sect1>
</article>