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<html>
<head>
<TITLE>Bitmap Format.</TITLE>
<meta http-equiv="content-type" content="text/html; charset=gb_2312-80">
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<p align="center"><font face="book antiqua" size="6" color="#0000ff">bmp format</font></p>
<div align="center"><center>
<table border="0" width="88%">
<tr>
<td width="100%"><b><p align="justify"><font face="book antiqua" size="6">table of
contents</font></p>
<font face="book antiqua" size="4"><p><a href="#_toc381201081">introduction</a> <br>
<a href="#_toc381201082">bitmap file format</a><br>
</font><font face="book antiqua" size="3">
<a
href="#_toc381201083">general</a> <br>
<a
href="#_toc381201084">bmp contents</a> <br>
</font><font face="book antiqua" size="4"><a href="#_toc381201085">field details </a><br>
</font><font face="book antiqua" size="3">
<a
href="#_toc381201086">height field </a><br>
<a
href="#_toc381201087">bits per pixel field</a> <br>
<a
href="#_toc381201088">compression field</a> <br>
<a
href="#_toc381201089">colors field</a> <br>
<a
href="#_toc381201090">important colors field</a> </font><u><font face="book antiqua"
size="4">
</font></u><font face="book antiqua" size="6"><a name="_toc381201081"><p>introduction</a>
</font></b><font face="book antiqua" size="3"><p align="justify">this document describes
the microsoft windows and ibm os/2 picture bitmap files, called bitmaps or bmp files. most
of the descriptions of the bmp file concentrate on the microsoft windows bmp structures
like </font><font face="courier new" size="3">bmpinfoheader</font><font
face="book antiqua" size="3"> and </font><font face="courier new" size="3">bmpcoreinfo</font><font
face="book antiqua" size="3"> , but only a few describe the file contents on byte level.
this information is therefor only intended to be used in applications where direct reading
and writing of a bmp file is required.
</font><b><font face="ޅ" lang="zh-cn" size="6"><p align="justify"></font><font
face="book antiqua" size="6"><a name="_toc381201082">bitmap file format</a></p>
</font></b><font face="book antiqua" size="3"><p align="justify">the following chapters
contain the detailed information on the contents of the bmp file. first more general
information will be given regarding the byte order and file alignment. the second chapter
will concentrate on the byte-level contents of a bmp file. the third chapter will
elaborate on this chapter and explain some of the concepts - like compression - and/or
values in detail.</p>
</font><b><font face="ޅ" lang="zh-cn" size="5"><p></font><font face="book antiqua"
size="5"><a name="_toc381201083">general</a>
</font></b><font face="book antiqua" size="3"><p align="justify">the bmp file has been
created by microsoft and ibm and is therefor very strictly bound to the architecture of
the main hardware platform that both companies support: the ibm compatible pc. this means
that all values stored in the bmp file are in the intel format, sometimes also called the
little endian format because of the byte order that an intel processor uses internally to
store values.</p>
<p align="justify">the bmp files are the way, windows stores bit mapped images. the bmp
image data is bit packed but every line must end on a dword boundary - if that</font><font
face="ޅ" lang="zh-cn" size="3">s</font><font size="3"> </font><font
face="book antiqua" size="3">not the case, it must be padded with zeroes. bmp files are
stored bottom-up, that means that the first scan line is the bottom line. </p>
<p align="justify">the bmp format has four incarnations, two under windows (new and old)
and two under os/2, all are described here.</p>
</font><b><font face="ޅ" lang="zh-cn" size="5"><p></font><font face="book antiqua"
size="5"><a name="_toc381201084">bmp contents</a>
</font></b><font face="book antiqua" size="3"><p align="justify">the following table
contains a description of the contents of the bmp file. for every field, the file offset,
the length and the contents will be given. for a more detailed discussion, see the
following chapters.</p>
</font><table border="1" cellspacing="2" bordercolor="#000000" cellpadding="7" width="657">
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify">offset</b></font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify">field</b></font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify">size</b></font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify">contents</b></font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0000h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">identifier</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">2 bytes</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">the
characters identifying the bitmap. the following entries are possible:</p>
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify">B</font><font
face="book antiqua" size="3">m</font><font size="3"> </font><font face="book antiqua"
size="3">- windows 3.1x, 95, nt, </font><font size="3"></font><font face="book antiqua"
size="3">
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify">B</font><font
face="book antiqua" size="3">a</font><font size="3"> </font><font face="book antiqua"
size="3">- os/2 bitmap array
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify">C</font><font
face="book antiqua" size="3">i</font><font size="3"> </font><font face="book antiqua"
size="3">- os/2 color icon
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify">C</font><font
face="book antiqua" size="3">p</font><font size="3"> </font><font face="book antiqua"
size="3">- os/2 color pointer
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify">I</font><font
face="book antiqua" size="3">c</font><font size="3"> </font><font face="book antiqua"
size="3">- os/2 icon
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify">P</font><font
face="book antiqua" size="3">t</font><font size="3"> </font><font face="book antiqua"
size="3">- os/2 pointer</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0002h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">file
size</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">complete
file size in bytes.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0006h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">reserved</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">reserved
for later use.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">000ah</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bitmap
data offset</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">offset
from beginning of file to the beginning of the bitmap data.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">000eh</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bitmap
header size</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">length
of the bitmap info header used to describe the bitmap colors, compression, </font><font
size="3"> </font><font face="book antiqua" size="3">the following sizes are possible:</p>
<p align="justify">28h - windows 3.1x, 95, nt, </font><font size="3"></font><font
face="book antiqua" size="3"></p>
<p align="justify">0ch - os/2 1.x</p>
<p align="justify">f0h - os/2 2.x</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0012h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">width</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">horizontal
width of bitmap in pixels.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0016h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">height</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">vertical
height of bitmap in pixels.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">001ah</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">planes</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 word</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">number
of planes in this bitmap.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">001ch</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bits
per pixel</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 word</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">bits
per pixel used to store palette entry information. this also identifies in an indirect way
the number of possible colors. possible values are:</p>
<p align="justify">1 - monochrome bitmap</p>
<p align="justify">4 - 16 color bitmap</p>
<p align="justify">8 - 256 color bitmap</p>
<p align="justify">16 - 16bit (high color) bitmap</p>
<p align="justify">24 - 24bit (true color) bitmap</p>
<p align="justify">32 - 32bit (true color) bitmap</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">001eh</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">compression</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">compression
specifications. the following values are possible:</p>
<p align="justify">0 - none (also identified by bi_rgb)</p>
<p align="justify">1 - rle 8-bit / pixel (also identified by bi_rle4)</p>
<p align="justify">2 - rle 4-bit / pixel (also identified by bi_rle8)</p>
<p align="justify">3 - bitfields (also identified by bi_bitfields)</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0022h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bitmap
data size</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">size of
the bitmap data in bytes. this number must be rounded to the next 4 byte boundary.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0026h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">hresolution</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">horizontal
resolution expressed in pixel per meter.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">002ah</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">vresolution</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">vertical
resolution expressed in pixels per meter.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">002eh</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">colors</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">number
of colors used by this bitmap. for a 8-bit / pixel bitmap this will be 100h or 256.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0032h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">important
colors</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">number
of important colors. this number will be equal to the number of colors when every color is
important.</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0036h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">palette</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">n * 4
byte</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">the
palette specification. for every entry in the palette four bytes are used to describe the
rgb values of the color in the following way:</p>
<p align="justify">1 byte for blue component</p>
<HR><H3>Transfer interrupted!</H3>
p>
<p align="justify">1 byte for red component</p>
<p align="justify">1 byte filler which is set to 0 (zero)</font></td>
</tr>
<tr>
<td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0436h</font></td>
<td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bitmap
data</font></td>
<td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">x bytes</font></td>
<td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">depending
on the compression specifications, this field contains all the bitmap data bytes which
represent indices in the color palette.</font></td>
</tr>
</table>
<font face="ޅ" lang="zh-cn" size="3"><p align="justify"></p>
</font><font face="book antiqua" size="3"><i><b><p align="justify">note:</b> the following
sizes were used in the specification above: </p>
</i></font><table border="1" cellspacing="2" bordercolor="#000000" cellpadding="7"
width="226">
<tr>
<td width="30%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify">size</b></font></td>
<td width="32%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify"># bytes</b></font></td>
<td width="37%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify">sign</b></font></td>
</tr>
<tr>
<td width="30%" valign="top"><font face="book antiqua" size="3"><p align="justify">char</font></td>
<td width="32%" valign="top"><font face="book antiqua" size="3"><p align="justify">1</font></td>
<td width="37%" valign="top"><font face="book antiqua" size="3"><p align="justify">signed</font></td>
</tr>
<tr>
<td width="30%" valign="top"><font face="book antiqua" size="3"><p align="justify">word</font></td>
<td width="32%" valign="top"><font face="book antiqua" size="3"><p align="justify">2</font></td>
<td width="37%" valign="top"><font face="book antiqua" size="3"><p align="justify">unsigned</font></td>
</tr>
<tr>
<td width="30%" valign="top"><font face="book antiqua" size="3"><p align="justify">dword</font></td>
<td width="32%" valign="top"><font face="book antiqua" size="3"><p align="justify">4</font></td>
<td width="37%" valign="top"><font face="book antiqua" size="3"><p align="justify">unsigned</font></td>
</tr>
</table>
<b><font face="ޅ" lang="zh-cn" size="6"><p align="justify"></font><font
face="book antiqua" size="6"><a name="_toc381201085">field details</a></p>
</font></b><font face="book antiqua" size="3"><p align="justify">some of the fields
require some more information. the following chapters will try to provide this
information:</p>
</font><b><font face="ޅ" lang="zh-cn" size="5"><p></font><font face="book antiqua"
size="5"><a name="_toc381201086">height field</a></p>
</font></b><font face="book antiqua" size="3"><p align="justify">the <i>height</i> field
identifies the height of the bitmap in pixels. in other words, it describes the number of
scan lines of the bitmap. if this field is negative, indicating a top-down dib, the <i>compression</i>
field must be either bi_rgb or bi_bitfields. top-down dibs cannot be compressed.</p>
</font><b><font face="ޅ" lang="zh-cn" size="5"><p></font><font face="book antiqua"
size="5"><a name="_toc381201087">bits per pixel field</a></p>
</font></b><font face="book antiqua" size="3"><p align="justify">the <i>bits per pixel</i>
(bbp) field of the bitmap file determines the number of bits that define each pixel and
the maximum number of colors in the bitmap.</p>
</font><font face="ޅ" lang="zh-cn" size="3"><ul>
</font><font face="book antiqua" size="3"><b>
<li>when this field is equal to 1.</b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the bitmap is monochrome, and
the palette contains two entries. each bit in the bitmap array represents a pixel. if the
bit is clear, the pixel is displayed with the color of the first entry in the palette; if
the bit is set, the pixel has the color of the second entry in the table.</p>
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify"></p>
</dir>
</dir>
<ul>
</font><font face="book antiqua" size="3"><b>
<li>when this field is equal to 4.</b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
16 colors, and the palette contains up to 16 entries. each pixel in the bitmap is
represented by a 4-bit index into the palette. for example, if the first byte in the
bitmap is 1fh, the byte represents two pixels. the first pixel contains the color in the
second palette entry, and the second pixel contains the color in the sixteenth palette
entry.</p>
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify"></p>
</dir>
</dir>
<ul>
</font><font face="book antiqua" size="3"><b>
<li>when this field is equal to 8.</b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
256 colors, and the palette contains up to 256 entries. in this case, each byte in the
array represents a single pixel.</p>
<p align="justify"></font><font size="3"></font><font face="book antiqua" size="3"></p>
</dir>
</dir>
<ul>
<b>
<li>when this field is equal to 16.</b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
2^16 colors. if the <i>compression</i> field of the bitmap file is set to bi_rgb, the <i>palette</i>
field does not contain any entries. each word in the bitmap array represents a single
pixel. the relative intensities of red, green, and blue are represented with 5 bits for
each color component. the value for blue is in the least significant 5 bits, followed by 5
bits each for green and red, respectively. the most significant bit is not used.</p>
<p align="justify">if the <i>compression</i> field of the bitmap file is set to
bi_bitfields, the <i>palette</i> field contains three dword color masks that specify the
red, green, and blue components, respectively, of each pixel. each word in the bitmap
array represents a single pixel.</p>
<b><p align="justify">windows nt specific:</b> when the <i>compression</i> field is set to
bi_bitfields, bits set in each dword mask must be contiguous and should not overlap the
bits of another mask. all the bits in the pixel do not have to be used. </p>
<b><p align="justify">windows 95 specific:</b> when the <i>compression</i> field is set to
bi_bitfields, windows 95 supports only the following 16bpp color masks: a 5-5-5 16-bit
image, where the blue mask is 0x001f, the green mask is 0x03e0, and the red mask is
0x7c00; and a 5-6-5 16-bit image, where the blue mask is 0x001f, the green mask is 0x07e0,
and the red mask is 0xf800.</p>
<p align="justify"></font><font size="3"></font><font face="book antiqua" size="3"></p>
</dir>
</dir>
<ul>
<b>
<li>when this field is equal to 24.</b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
2^24 colors, and the <i>palette</i> field does not contain any entries. each 3-byte
triplet in the bitmap array represents the relative intensities of blue, green, and red,
respectively, for a pixel.</p>
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify"></p>
</dir>
</dir>
<ul>
</font><font face="book antiqua" size="3"><b>
<li>when this field is equal to 32.</b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
2^32 colors. if the <i>compression</i> field of the bitmap is set to bi_rgb, the <i>palette</i>
field does not contain any entries. each dword in the bitmap array represents the relative
intensities of blue, green, and red, respectively, for a pixel. the high byte in each
dword is not used.</p>
<p align="justify">if the <i>compression</i> field of the bitmap is set to bi_bitfields,
the palette field contains three dword color masks that specify the red, green, and blue
components, respectively, of each pixel. each dword in the bitmap array represents a
single pixel.</p>
<b><p align="justify">windows nt specific:</b> when the <i>compression</i> field is set to
bi_bitfields, bits set in each dword mask must be contiguous and should not overlap the
bits of another mask. all the bits in the pixel do not have to be used. </p>
<b><p align="justify">windows 95 specific:</b> when the <i>compression</i> field is set to
bi_bitfields, windows 95 supports only the following 32bpp color mask: the blue mask is
0x000000ff, the green mask is 0x0000ff00, and the red mask is 0x00ff0000.</font></p>
</dir>
</dir>
<b><font face="ޅ" lang="zh-cn" size="5"><p></font><font face="book antiqua" size="5"><a
name="_toc381201088">compression field</a></p>
</font></b><font face="book antiqua" size="3"><p align="justify">the <i>compression</i>
field specifies the way the bitmap data is stored in the file. this information together
with the <i>bits per pixel</i> (<i>bpp</i>) field identifies the compression algorithm to
follow.</p>
<p align="justify">the following values are possible in this field:</p>
</font><table border="1" cellspacing="2" bordercolor="#000000" cellpadding="7" width="657">
<tr>
<td width="18%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify">value</b></font></td>
<td width="82%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
align="justify">meaning</b></font></td>
</tr>
<tr>
<td width="18%" valign="top"><font face="book antiqua" size="3"><p align="justify">bi_rgb</font></td>
<td width="82%" valign="top"><font face="book antiqua" size="3"><p align="justify">an
uncompressed format.</font></td>
</tr>
<tr>
<td width="18%" valign="top"><f>
<HR>
lign="justify">bi_rle4</font></td>
<td width="82%" valign="top"><font face="book antiqua" size="3"><p align="justify">an rle
format for bitmaps with 4 bits per pixel. the compression format is a two-byte format
consisting of a count byte followed by two word-length color indices. for more
information, see the following remarks section.</font></td>
</tr>
<tr>
<td width="18%" valign="top"><font face="book antiqua" size="3"><p align="justify">bi_rle8</font></td>
<td width="82%" valign="top"><font face="book antiqua" size="3"><p align="justify">a
run-length encoded (rle) format for bitmaps with 8 bits per pixel. the compression format
is a two-byte format consisting of a count byte followed by a byte containing a color
index. for more information, see the following remarks section.</font></td>
</tr>
<tr>
<td width="18%" valign="top"><font face="book antiqua" size="3"><p align="justify">bi_bitfields</font></td>
<td width="82%" valign="top"><font face="book antiqua" size="3"><p align="justify">specifies
that the bitmap is not compressed and that the color table consists of three double word
color masks that specify the red, green, and blue components, respectively, of each pixel.
this is valid when used with 16- and 32- bits-per-pixel bitmaps.</font></td>
</tr>
</table>
<font face="book antiqua" size="3"><p align="justify">when the compression field is
bi_rle8, the bitmap is compressed by using a run-length encoding (rle) format for an 8-bit
bitmap. this format can be compressed in encoded or absolute modes. both modes can occur
anywhere in the same bitmap.</p>
<ul>
<b>
<li>encoded mode consists of two bytes: </b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the first byte specifies the
number of consecutive pixels to be drawn using the color index contained in the second
byte. in addition, the first byte of the pair can be set to zero to indicate an escape
that denotes an end of line, end of bitmap, or delta. the interpretation of the escape
depends on the value of the second byte of the pair, which can be one of the following:</font></p>
</dir>
</dir>
<table cellspacing="0" border="0" cellpadding="7" width="602">
<tr>
<td width="9%" valign="top"><font face="book antiqua" size="3"><p align="justify">0</font></td>
<td width="91%" valign="top"><font face="book antiqua" size="3"><p align="justify">end of
line.</font></td>
</tr>
<tr>
<td width="9%" valign="top"><font face="book antiqua" size="3"><p align="justify">1</font></td>
<td width="91%" valign="top"><font face="book antiqua" size="3"><p align="justify">end of
bitmap.</font></td>
</tr>
<tr>
<td width="9%" valign="top"><font face="book antiqua" size="3"><p align="justify">2</font></td>
<td width="91%" valign="top"><font face="book antiqua" size="3"><p align="justify">delta.
the two bytes following the escape contain unsigned values indicating the horizontal and
vertical offsets of the next pixel from the current position.</font></td>
</tr>
</table>
<font face="ޅ" lang="zh-cn" size="3"><ul>
</font><font face="book antiqua" size="3"><b>
<li>absolute mode.</b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the first byte is zero and
the second byte is a value in the range 03h through ffh. the second byte represents the
number of bytes that follow, each of which contains the color index of a single pixel.
when the second byte is 2 or less, the escape has the same meaning as in encoded mode. in
absolute mode, each run must be aligned on a word boundary.</p>
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify"></p>
<p align="justify"></font></p>
</dir>
</dir>
<font face="book antiqua" size="3"><p align="justify">the following example shows the
hexadecimal values of an 8-bit compressed bitmap.</p>
</font><font face="courier new" size="3"><p align="justify">03 04 05 06 00 03 45 56 67 00
02 78 00 02 05 01 02 78 00 00 09 1e 00 01</p>
</font><font face="book antiqua" size="3"><p align="justify">this bitmap would expand as
follows (two-digit values represent a color index for a single pixel):</p>
</font><font face="courier new" size="3"><p align="justify">04 04 04</p>
<p align="justify">06 06 06 06 06</p>
<p align="justify">45 56 67</p>
<p align="justify">78 78</p>
<p align="justify">move current position 5 right and 1 down</p>
<p align="justify">78 78</p>
<p align="justify">end of line</p>
<p align="justify">1e 1e 1e 1e 1e 1e 1e 1e 1e</p>
<p align="justify">end of rle bitmap</p>
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify"></p>
</font><font face="book antiqua" size="3"><p align="justify">when the compression field is
bi_rle4, the bitmap is compressed by using a run-length encoding format for a 4-bit
bitmap, which also uses encoded and absolute modes:</p>
<ul>
<b>
<li>in encoded mode.</b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the first byte of the pair
contains the number of pixels to be drawn using the color indices in the second byte. the
second byte contains two color indices, one in its high-order four bits and one in its
low-order four bits. the first of the pixels is drawn using the color specified by the
high-order four bits, the second is drawn using the color in the low-order four bits, the
third is drawn using the color in the high-order four bits, and so on, until all the
pixels specified by the first byte have been drawn.</p>
</font><font face="ޅ" lang="zh-cn" size="3">
</dir>
</dir>
<ul>
</font><font face="book antiqua" size="3"><b>
<li>in absolute mode. </b></font></li>
</ul>
<font face="ޅ" lang="zh-cn" size="3"><dir>
<dir>
</font><font face="book antiqua" size="3"><p align="justify">the first byte is zero, the
second byte contains the number of color indices that follow, and subsequent bytes contain
color indices in their high- and low-order four bits, one color index for each pixel. in
absolute mode, each run must be aligned on a word boundary. </p>
<p align="justify">the end-of-line, end-of-bitmap, and delta escapes described for bi_rle8
also apply to bi_rle4 compression.</p>
</font><font face="ޅ" lang="zh-cn" size="3"><p align="justify"></font></p>
</dir>
</dir>
<font face="book antiqua" size="3"><p align="justify">the following example shows the
hexadecimal values of a 4-bit compressed bitmap.</p>
</font><font face="courier new" size="3"><p align="justify">03 04 05 06 00 06 45 56 67 00
04 78 00 02 05 01 04 78 00 00 09 1e 00 01</p>
</font><font face="book antiqua" size="3"><p align="justify">this bitmap would expand as
follows (single-digit values represent a color index for a single pixel):</p>
</font><font face="courier new" size="3"><p align="justify">0 4 0</p>
<p align="justify">0 6 0 6 0</p>
<p align="justify">4 5 5 6 6 7</p>
<p align="justify">7 8 7 8</p>
<p align="justify">move current position 5 right and 1 down</p>
<p align="justify">7 8 7 8</p>
<p align="justify">end of line</p>
<p align="justify">1 e 1 e 1 e 1 e 1</p>
<p align="justify">end of rle bitmap</p>
</font><b><font face="ޅ" lang="zh-cn" size="5"><p></font><font face="book antiqua"
size="5"><a name="_toc381201089">colors field</a></p>
</font></b><font face="book antiqua" size="3"><p align="justify">the <i>colors</i> field
specifies the number of color indices in the color table that are actually used by the
bitmap. if this value is zero, the bitmap uses the maximum number of colors corresponding
to the value of the <i>bbp</i> field for the compression mode specified by the <i>compression</i>
field. </p>
<p align="justify">if the <i>colors</i> field is nonzero and the <i>bbp</i> field less
than 16, the <i>colors</i> field specifies the actual number of colors the graphics engine
or device driver accesses. </p>
<p align="justify">if the <i>bbp</i> field is 16 or greater, then <i>colors</i> field
specifies the size of the color table used to optimize performance of windows color
palettes. </p>
<p align="justify">if <i>bbp</i> equals 16 or 32, the optimal color palette starts
immediately following the three double word masks.</p>
<p align="justify">if the bitmap is a packed bitmap (a bitmap in which the bitmap array
immediately follows the bitmap header and which is referenced by a single pointer), the <i>colors</i>
field must be either 0 or the actual size of the color table. </p>
</font><b><font face="ޅ" lang="zh-cn" size="5"><p></font><font face="book antiqua"
size="5"><a name="_toc381201090">important colors field</a></p>
</font></b><font face="arial" size="3"><p align="justify">the <i>important colors</i>
field s</font><font face="book antiqua" size="3">pecifies the number of color indices that
are considered important for displaying the bitmap. if this value is zero, all colors are
important. </font></td>
</tr>
</table>
</center></div>
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