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13 <p align="center"><font face="book antiqua" size="6" color="#0000ff">bmp format</font></p>
14 <div align="center"><center>
16 <table border="0" width="88%">
18 <td width="100%"><b><p align="justify"><font face="book antiqua" size="6">table of
20 <font face="book antiqua" size="4"><p><a href="#_toc381201081">introduction</a> <br>
21 <a href="#_toc381201082">bitmap file format</a><br>
22 </font><font face="book antiqua" size="3">
23 <a
24 href="#_toc381201083">general</a> <br>
25 <a
26 href="#_toc381201084">bmp contents</a> <br>
27 </font><font face="book antiqua" size="4"><a href="#_toc381201085">field details </a><br>
28 </font><font face="book antiqua" size="3">
29 <a
30 href="#_toc381201086">height field </a><br>
31 <a
32 href="#_toc381201087">bits per pixel field</a> <br>
33 <a
34 href="#_toc381201088">compression field</a> <br>
35 <a
36 href="#_toc381201089">colors field</a> <br>
37 <a
38 href="#_toc381201090">important colors field</a> </font><u><font face="book antiqua"
40 </font></u><font face="book antiqua" size="6"><a name="_toc381201081"><p>introduction</a>
41 </font></b><font face="book antiqua" size="3"><p align="justify">this document describes
42 the microsoft windows and ibm os/2 picture bitmap files, called bitmaps or bmp files. most
43 of the descriptions of the bmp file concentrate on the microsoft windows bmp structures
44 like </font><font face="courier new" size="3">bmpinfoheader</font><font
45 face="book antiqua" size="3"> and </font><font face="courier new" size="3">bmpcoreinfo</font><font
46 face="book antiqua" size="3"> , but only a few describe the file contents on byte level.
47 this information is therefor only intended to be used in applications where direct reading
48 and writing of a bmp file is required.
49 </font><b><font face="ÝðÞ
\85" lang="zh-cn" size="6"><p align="justify"></font><font
50 face="book antiqua" size="6"><a name="_toc381201082">bitmap file format</a></p>
51 </font></b><font face="book antiqua" size="3"><p align="justify">the following chapters
52 contain the detailed information on the contents of the bmp file. first more general
53 information will be given regarding the byte order and file alignment. the second chapter
54 will concentrate on the byte-level contents of a bmp file. the third chapter will
55 elaborate on this chapter and explain some of the concepts - like compression - and/or
57 </font><b><font face="ÝðÞ
\85" lang="zh-cn" size="5"><p></font><font face="book antiqua"
58 size="5"><a name="_toc381201083">general</a>
59 </font></b><font face="book antiqua" size="3"><p align="justify">the bmp file has been
60 created by microsoft and ibm and is therefor very strictly bound to the architecture of
61 the main hardware platform that both companies support: the ibm compatible pc. this means
62 that all values stored in the bmp file are in the intel format, sometimes also called the
63 little endian format because of the byte order that an intel processor uses internally to
65 <p align="justify">the bmp files are the way, windows stores bit mapped images. the bmp
66 image data is bit packed but every line must end on a dword boundary - if that</font><font
67 face="ÝðÞ
\85" lang="zh-cn" size="3">Æs</font><font size="3"> </font><font
68 face="book antiqua" size="3">not the case, it must be padded with zeroes. bmp files are
69 stored bottom-up, that means that the first scan line is the bottom line. </p>
70 <p align="justify">the bmp format has four incarnations, two under windows (new and old)
71 and two under os/2, all are described here.</p>
72 </font><b><font face="ÝðÞ
\85" lang="zh-cn" size="5"><p></font><font face="book antiqua"
73 size="5"><a name="_toc381201084">bmp contents</a>
74 </font></b><font face="book antiqua" size="3"><p align="justify">the following table
75 contains a description of the contents of the bmp file. for every field, the file offset,
76 the length and the contents will be given. for a more detailed discussion, see the
77 following chapters.</p>
78 </font><table border="1" cellspacing="2" bordercolor="#000000" cellpadding="7" width="657">
80 <td width="10%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
81 align="justify">offset</b></font></td>
82 <td width="16%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
83 align="justify">field</b></font></td>
84 <td width="14%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
85 align="justify">size</b></font></td>
86 <td width="61%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
87 align="justify">contents</b></font></td>
90 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0000h</font></td>
91 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">identifier</font></td>
92 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">2 bytes</font></td>
93 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">the
94 characters identifying the bitmap. the following entries are possible:</p>
95 </font><font face="ÝðÞ
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96 face="book antiqua" size="3">m</font><font size="3">í¯ </font><font face="book antiqua"
97 size="3">- windows 3.1x, 95, nt, </font><font size="3">í¡</font><font face="book antiqua"
99 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3"><p align="justify">æB</font><font
100 face="book antiqua" size="3">a</font><font size="3">í¯ </font><font face="book antiqua"
101 size="3">- os/2 bitmap array
102 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3"><p align="justify">æC</font><font
103 face="book antiqua" size="3">i</font><font size="3">í¯ </font><font face="book antiqua"
104 size="3">- os/2 color icon
105 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3"><p align="justify">æC</font><font
106 face="book antiqua" size="3">p</font><font size="3">í¯ </font><font face="book antiqua"
107 size="3">- os/2 color pointer
108 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3"><p align="justify">æI</font><font
109 face="book antiqua" size="3">c</font><font size="3">í¯ </font><font face="book antiqua"
111 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3"><p align="justify">æP</font><font
112 face="book antiqua" size="3">t</font><font size="3">í¯ </font><font face="book antiqua"
113 size="3">- os/2 pointer</font></td>
116 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0002h</font></td>
117 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">file
119 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
120 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">complete
121 file size in bytes.</font></td>
124 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0006h</font></td>
125 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">reserved</font></td>
126 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
127 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">reserved
128 for later use.</font></td>
131 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">000ah</font></td>
132 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bitmap
133 data offset</font></td>
134 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
135 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">offset
136 from beginning of file to the beginning of the bitmap data.</font></td>
139 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">000eh</font></td>
140 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bitmap
141 header size</font></td>
142 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
143 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">length
144 of the bitmap info header used to describe the bitmap colors, compression, </font><font
145 size="3">í¡ </font><font face="book antiqua" size="3">the following sizes are possible:</p>
146 <p align="justify">28h - windows 3.1x, 95, nt, </font><font size="3">í¡</font><font
147 face="book antiqua" size="3"></p>
148 <p align="justify">0ch - os/2 1.x</p>
149 <p align="justify">f0h - os/2 2.x</font></td>
152 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0012h</font></td>
153 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">width</font></td>
154 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
155 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">horizontal
156 width of bitmap in pixels.</font></td>
159 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0016h</font></td>
160 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">height</font></td>
161 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
162 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">vertical
163 height of bitmap in pixels.</font></td>
166 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">001ah</font></td>
167 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">planes</font></td>
168 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 word</font></td>
169 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">number
170 of planes in this bitmap.</font></td>
173 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">001ch</font></td>
174 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bits
175 per pixel</font></td>
176 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 word</font></td>
177 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">bits
178 per pixel used to store palette entry information. this also identifies in an indirect way
179 the number of possible colors. possible values are:</p>
180 <p align="justify">1 - monochrome bitmap</p>
181 <p align="justify">4 - 16 color bitmap</p>
182 <p align="justify">8 - 256 color bitmap</p>
183 <p align="justify">16 - 16bit (high color) bitmap</p>
184 <p align="justify">24 - 24bit (true color) bitmap</p>
185 <p align="justify">32 - 32bit (true color) bitmap</font></td>
188 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">001eh</font></td>
189 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">compression</font></td>
190 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
191 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">compression
192 specifications. the following values are possible:</p>
193 <p align="justify">0 - none (also identified by bi_rgb)</p>
194 <p align="justify">1 - rle 8-bit / pixel (also identified by bi_rle4)</p>
195 <p align="justify">2 - rle 4-bit / pixel (also identified by bi_rle8)</p>
196 <p align="justify">3 - bitfields (also identified by bi_bitfields)</font></td>
199 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0022h</font></td>
200 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bitmap
201 data size</font></td>
202 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
203 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">size of
204 the bitmap data in bytes. this number must be rounded to the next 4 byte boundary.</font></td>
207 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0026h</font></td>
208 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">hresolution</font></td>
209 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
210 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">horizontal
211 resolution expressed in pixel per meter.</font></td>
214 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">002ah</font></td>
215 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">vresolution</font></td>
216 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
217 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">vertical
218 resolution expressed in pixels per meter.</font></td>
221 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">002eh</font></td>
222 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">colors</font></td>
223 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
224 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">number
225 of colors used by this bitmap. for a 8-bit / pixel bitmap this will be 100h or 256.</font></td>
228 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0032h</font></td>
229 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">important
231 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">1 dword</font></td>
232 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">number
233 of important colors. this number will be equal to the number of colors when every color is
234 important.</font></td>
237 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0036h</font></td>
238 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">palette</font></td>
239 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">n * 4
241 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">the
242 palette specification. for every entry in the palette four bytes are used to describe the
243 rgb values of the color in the following way:</p>
244 <p align="justify">1 byte for blue component</p>
245 <HR><H3>Transfer interrupted!</H3>
247 <p align="justify">1 byte for red component</p>
248 <p align="justify">1 byte filler which is set to 0 (zero)</font></td>
251 <td width="10%" valign="top"><font face="book antiqua" size="3"><p align="justify">0436h</font></td>
252 <td width="16%" valign="top"><font face="book antiqua" size="3"><p align="justify">bitmap
254 <td width="14%" valign="top"><font face="book antiqua" size="3"><p align="justify">x bytes</font></td>
255 <td width="61%" valign="top"><font face="book antiqua" size="3"><p align="justify">depending
256 on the compression specifications, this field contains all the bitmap data bytes which
257 represent indices in the color palette.</font></td>
260 <font face="ÝðÞ
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261 </font><font face="book antiqua" size="3"><i><b><p align="justify">note:</b> the following
262 sizes were used in the specification above: </p>
263 </i></font><table border="1" cellspacing="2" bordercolor="#000000" cellpadding="7"
266 <td width="30%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
267 align="justify">size</b></font></td>
268 <td width="32%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
269 align="justify"># bytes</b></font></td>
270 <td width="37%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
271 align="justify">sign</b></font></td>
274 <td width="30%" valign="top"><font face="book antiqua" size="3"><p align="justify">char</font></td>
275 <td width="32%" valign="top"><font face="book antiqua" size="3"><p align="justify">1</font></td>
276 <td width="37%" valign="top"><font face="book antiqua" size="3"><p align="justify">signed</font></td>
279 <td width="30%" valign="top"><font face="book antiqua" size="3"><p align="justify">word</font></td>
280 <td width="32%" valign="top"><font face="book antiqua" size="3"><p align="justify">2</font></td>
281 <td width="37%" valign="top"><font face="book antiqua" size="3"><p align="justify">unsigned</font></td>
284 <td width="30%" valign="top"><font face="book antiqua" size="3"><p align="justify">dword</font></td>
285 <td width="32%" valign="top"><font face="book antiqua" size="3"><p align="justify">4</font></td>
286 <td width="37%" valign="top"><font face="book antiqua" size="3"><p align="justify">unsigned</font></td>
289 <b><font face="ÝðÞ
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290 face="book antiqua" size="6"><a name="_toc381201085">field details</a></p>
291 </font></b><font face="book antiqua" size="3"><p align="justify">some of the fields
292 require some more information. the following chapters will try to provide this
294 </font><b><font face="ÝðÞ
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295 size="5"><a name="_toc381201086">height field</a></p>
296 </font></b><font face="book antiqua" size="3"><p align="justify">the <i>height</i> field
297 identifies the height of the bitmap in pixels. in other words, it describes the number of
298 scan lines of the bitmap. if this field is negative, indicating a top-down dib, the <i>compression</i>
299 field must be either bi_rgb or bi_bitfields. top-down dibs cannot be compressed.</p>
300 </font><b><font face="ÝðÞ
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301 size="5"><a name="_toc381201087">bits per pixel field</a></p>
302 </font></b><font face="book antiqua" size="3"><p align="justify">the <i>bits per pixel</i>
303 (bbp) field of the bitmap file determines the number of bits that define each pixel and
304 the maximum number of colors in the bitmap.</p>
305 </font><font face="ÝðÞ
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306 </font><font face="book antiqua" size="3"><b>
307 <li>when this field is equal to 1.</b></font></li>
309 <font face="ÝðÞ
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311 </font><font face="book antiqua" size="3"><p align="justify">the bitmap is monochrome, and
312 the palette contains two entries. each bit in the bitmap array represents a pixel. if the
313 bit is clear, the pixel is displayed with the color of the first entry in the palette; if
314 the bit is set, the pixel has the color of the second entry in the table.</p>
315 </font><font face="ÝðÞ
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319 </font><font face="book antiqua" size="3"><b>
320 <li>when this field is equal to 4.</b></font></li>
322 <font face="ÝðÞ
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324 </font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
325 16 colors, and the palette contains up to 16 entries. each pixel in the bitmap is
326 represented by a 4-bit index into the palette. for example, if the first byte in the
327 bitmap is 1fh, the byte represents two pixels. the first pixel contains the color in the
328 second palette entry, and the second pixel contains the color in the sixteenth palette
330 </font><font face="ÝðÞ
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334 </font><font face="book antiqua" size="3"><b>
335 <li>when this field is equal to 8.</b></font></li>
337 <font face="ÝðÞ
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339 </font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
340 256 colors, and the palette contains up to 256 entries. in this case, each byte in the
341 array represents a single pixel.</p>
342 <p align="justify"></font><font size="3">íí</font><font face="book antiqua" size="3"></p>
347 <li>when this field is equal to 16.</b></font></li>
349 <font face="ÝðÞ
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351 </font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
352 2^16 colors. if the <i>compression</i> field of the bitmap file is set to bi_rgb, the <i>palette</i>
353 field does not contain any entries. each word in the bitmap array represents a single
354 pixel. the relative intensities of red, green, and blue are represented with 5 bits for
355 each color component. the value for blue is in the least significant 5 bits, followed by 5
356 bits each for green and red, respectively. the most significant bit is not used.</p>
357 <p align="justify">if the <i>compression</i> field of the bitmap file is set to
358 bi_bitfields, the <i>palette</i> field contains three dword color masks that specify the
359 red, green, and blue components, respectively, of each pixel. each word in the bitmap
360 array represents a single pixel.</p>
361 <b><p align="justify">windows nt specific:</b> when the <i>compression</i> field is set to
362 bi_bitfields, bits set in each dword mask must be contiguous and should not overlap the
363 bits of another mask. all the bits in the pixel do not have to be used. </p>
364 <b><p align="justify">windows 95 specific:</b> when the <i>compression</i> field is set to
365 bi_bitfields, windows 95 supports only the following 16bpp color masks: a 5-5-5 16-bit
366 image, where the blue mask is 0x001f, the green mask is 0x03e0, and the red mask is
367 0x7c00; and a 5-6-5 16-bit image, where the blue mask is 0x001f, the green mask is 0x07e0,
368 and the red mask is 0xf800.</p>
369 <p align="justify"></font><font size="3">íí</font><font face="book antiqua" size="3"></p>
374 <li>when this field is equal to 24.</b></font></li>
376 <font face="ÝðÞ
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378 </font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
379 2^24 colors, and the <i>palette</i> field does not contain any entries. each 3-byte
380 triplet in the bitmap array represents the relative intensities of blue, green, and red,
381 respectively, for a pixel.</p>
382 </font><font face="ÝðÞ
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386 </font><font face="book antiqua" size="3"><b>
387 <li>when this field is equal to 32.</b></font></li>
389 <font face="ÝðÞ
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391 </font><font face="book antiqua" size="3"><p align="justify">the bitmap has a maximum of
392 2^32 colors. if the <i>compression</i> field of the bitmap is set to bi_rgb, the <i>palette</i>
393 field does not contain any entries. each dword in the bitmap array represents the relative
394 intensities of blue, green, and red, respectively, for a pixel. the high byte in each
395 dword is not used.</p>
396 <p align="justify">if the <i>compression</i> field of the bitmap is set to bi_bitfields,
397 the palette field contains three dword color masks that specify the red, green, and blue
398 components, respectively, of each pixel. each dword in the bitmap array represents a
400 <b><p align="justify">windows nt specific:</b> when the <i>compression</i> field is set to
401 bi_bitfields, bits set in each dword mask must be contiguous and should not overlap the
402 bits of another mask. all the bits in the pixel do not have to be used. </p>
403 <b><p align="justify">windows 95 specific:</b> when the <i>compression</i> field is set to
404 bi_bitfields, windows 95 supports only the following 32bpp color mask: the blue mask is
405 0x000000ff, the green mask is 0x0000ff00, and the red mask is 0x00ff0000.</font></p>
408 <b><font face="ÝðÞ
\85" lang="zh-cn" size="5"><p></font><font face="book antiqua" size="5"><a
409 name="_toc381201088">compression field</a></p>
410 </font></b><font face="book antiqua" size="3"><p align="justify">the <i>compression</i>
411 field specifies the way the bitmap data is stored in the file. this information together
412 with the <i>bits per pixel</i> (<i>bpp</i>) field identifies the compression algorithm to
414 <p align="justify">the following values are possible in this field:</p>
415 </font><table border="1" cellspacing="2" bordercolor="#000000" cellpadding="7" width="657">
417 <td width="18%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
418 align="justify">value</b></font></td>
419 <td width="82%" valign="top"><font face="book antiqua" size="3" color="#808080"><b><p
420 align="justify">meaning</b></font></td>
423 <td width="18%" valign="top"><font face="book antiqua" size="3"><p align="justify">bi_rgb</font></td>
424 <td width="82%" valign="top"><font face="book antiqua" size="3"><p align="justify">an
425 uncompressed format.</font></td>
428 <td width="18%" valign="top"><f>
430 lign="justify">bi_rle4</font></td>
431 <td width="82%" valign="top"><font face="book antiqua" size="3"><p align="justify">an rle
432 format for bitmaps with 4 bits per pixel. the compression format is a two-byte format
433 consisting of a count byte followed by two word-length color indices. for more
434 information, see the following remarks section.</font></td>
437 <td width="18%" valign="top"><font face="book antiqua" size="3"><p align="justify">bi_rle8</font></td>
438 <td width="82%" valign="top"><font face="book antiqua" size="3"><p align="justify">a
439 run-length encoded (rle) format for bitmaps with 8 bits per pixel. the compression format
440 is a two-byte format consisting of a count byte followed by a byte containing a color
441 index. for more information, see the following remarks section.</font></td>
444 <td width="18%" valign="top"><font face="book antiqua" size="3"><p align="justify">bi_bitfields</font></td>
445 <td width="82%" valign="top"><font face="book antiqua" size="3"><p align="justify">specifies
446 that the bitmap is not compressed and that the color table consists of three double word
447 color masks that specify the red, green, and blue components, respectively, of each pixel.
448 this is valid when used with 16- and 32- bits-per-pixel bitmaps.</font></td>
451 <font face="book antiqua" size="3"><p align="justify">when the compression field is
452 bi_rle8, the bitmap is compressed by using a run-length encoding (rle) format for an 8-bit
453 bitmap. this format can be compressed in encoded or absolute modes. both modes can occur
454 anywhere in the same bitmap.</p>
457 <li>encoded mode consists of two bytes: </b></font></li>
459 <font face="ÝðÞ
\85" lang="zh-cn" size="3"><dir>
461 </font><font face="book antiqua" size="3"><p align="justify">the first byte specifies the
462 number of consecutive pixels to be drawn using the color index contained in the second
463 byte. in addition, the first byte of the pair can be set to zero to indicate an escape
464 that denotes an end of line, end of bitmap, or delta. the interpretation of the escape
465 depends on the value of the second byte of the pair, which can be one of the following:</font></p>
468 <table cellspacing="0" border="0" cellpadding="7" width="602">
470 <td width="9%" valign="top"><font face="book antiqua" size="3"><p align="justify">0</font></td>
471 <td width="91%" valign="top"><font face="book antiqua" size="3"><p align="justify">end of
475 <td width="9%" valign="top"><font face="book antiqua" size="3"><p align="justify">1</font></td>
476 <td width="91%" valign="top"><font face="book antiqua" size="3"><p align="justify">end of
480 <td width="9%" valign="top"><font face="book antiqua" size="3"><p align="justify">2</font></td>
481 <td width="91%" valign="top"><font face="book antiqua" size="3"><p align="justify">delta.
482 the two bytes following the escape contain unsigned values indicating the horizontal and
483 vertical offsets of the next pixel from the current position.</font></td>
486 <font face="ÝðÞ
\85" lang="zh-cn" size="3"><ul>
487 </font><font face="book antiqua" size="3"><b>
488 <li>absolute mode.</b></font></li>
490 <font face="ÝðÞ
\85" lang="zh-cn" size="3"><dir>
492 </font><font face="book antiqua" size="3"><p align="justify">the first byte is zero and
493 the second byte is a value in the range 03h through ffh. the second byte represents the
494 number of bytes that follow, each of which contains the color index of a single pixel.
495 when the second byte is 2 or less, the escape has the same meaning as in encoded mode. in
496 absolute mode, each run must be aligned on a word boundary.</p>
497 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3"><p align="justify">íí</p>
498 <p align="justify"></font>íí</p>
501 <font face="book antiqua" size="3"><p align="justify">the following example shows the
502 hexadecimal values of an 8-bit compressed bitmap.</p>
503 </font><font face="courier new" size="3"><p align="justify">03 04 05 06 00 03 45 56 67 00
504 02 78 00 02 05 01 02 78 00 00 09 1e 00 01</p>
505 </font><font face="book antiqua" size="3"><p align="justify">this bitmap would expand as
506 follows (two-digit values represent a color index for a single pixel):</p>
507 </font><font face="courier new" size="3"><p align="justify">04 04 04</p>
508 <p align="justify">06 06 06 06 06</p>
509 <p align="justify">45 56 67</p>
510 <p align="justify">78 78</p>
511 <p align="justify">move current position 5 right and 1 down</p>
512 <p align="justify">78 78</p>
513 <p align="justify">end of line</p>
514 <p align="justify">1e 1e 1e 1e 1e 1e 1e 1e 1e</p>
515 <p align="justify">end of rle bitmap</p>
516 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3"><p align="justify">íí</p>
517 </font><font face="book antiqua" size="3"><p align="justify">when the compression field is
518 bi_rle4, the bitmap is compressed by using a run-length encoding format for a 4-bit
519 bitmap, which also uses encoded and absolute modes:</p>
522 <li>in encoded mode.</b></font></li>
524 <font face="ÝðÞ
\85" lang="zh-cn" size="3"><dir>
526 </font><font face="book antiqua" size="3"><p align="justify">the first byte of the pair
527 contains the number of pixels to be drawn using the color indices in the second byte. the
528 second byte contains two color indices, one in its high-order four bits and one in its
529 low-order four bits. the first of the pixels is drawn using the color specified by the
530 high-order four bits, the second is drawn using the color in the low-order four bits, the
531 third is drawn using the color in the high-order four bits, and so on, until all the
532 pixels specified by the first byte have been drawn.</p>
533 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3">
537 </font><font face="book antiqua" size="3"><b>
538 <li>in absolute mode. </b></font></li>
540 <font face="ÝðÞ
\85" lang="zh-cn" size="3"><dir>
542 </font><font face="book antiqua" size="3"><p align="justify">the first byte is zero, the
543 second byte contains the number of color indices that follow, and subsequent bytes contain
544 color indices in their high- and low-order four bits, one color index for each pixel. in
545 absolute mode, each run must be aligned on a word boundary. </p>
546 <p align="justify">the end-of-line, end-of-bitmap, and delta escapes described for bi_rle8
547 also apply to bi_rle4 compression.</p>
548 </font><font face="ÝðÞ
\85" lang="zh-cn" size="3"><p align="justify"></font>íí</p>
551 <font face="book antiqua" size="3"><p align="justify">the following example shows the
552 hexadecimal values of a 4-bit compressed bitmap.</p>
553 </font><font face="courier new" size="3"><p align="justify">03 04 05 06 00 06 45 56 67 00
554 04 78 00 02 05 01 04 78 00 00 09 1e 00 01</p>
555 </font><font face="book antiqua" size="3"><p align="justify">this bitmap would expand as
556 follows (single-digit values represent a color index for a single pixel):</p>
557 </font><font face="courier new" size="3"><p align="justify">0 4 0</p>
558 <p align="justify">0 6 0 6 0</p>
559 <p align="justify">4 5 5 6 6 7</p>
560 <p align="justify">7 8 7 8</p>
561 <p align="justify">move current position 5 right and 1 down</p>
562 <p align="justify">7 8 7 8</p>
563 <p align="justify">end of line</p>
564 <p align="justify">1 e 1 e 1 e 1 e 1</p>
565 <p align="justify">end of rle bitmap</p>
566 </font><b><font face="ÝðÞ
\85" lang="zh-cn" size="5"><p></font><font face="book antiqua"
567 size="5"><a name="_toc381201089">colors field</a></p>
568 </font></b><font face="book antiqua" size="3"><p align="justify">the <i>colors</i> field
569 specifies the number of color indices in the color table that are actually used by the
570 bitmap. if this value is zero, the bitmap uses the maximum number of colors corresponding
571 to the value of the <i>bbp</i> field for the compression mode specified by the <i>compression</i>
573 <p align="justify">if the <i>colors</i> field is nonzero and the <i>bbp</i> field less
574 than 16, the <i>colors</i> field specifies the actual number of colors the graphics engine
575 or device driver accesses. </p>
576 <p align="justify">if the <i>bbp</i> field is 16 or greater, then <i>colors</i> field
577 specifies the size of the color table used to optimize performance of windows color
579 <p align="justify">if <i>bbp</i> equals 16 or 32, the optimal color palette starts
580 immediately following the three double word masks.</p>
581 <p align="justify">if the bitmap is a packed bitmap (a bitmap in which the bitmap array
582 immediately follows the bitmap header and which is referenced by a single pointer), the <i>colors</i>
583 field must be either 0 or the actual size of the color table. </p>
584 </font><b><font face="ÝðÞ
\85" lang="zh-cn" size="5"><p></font><font face="book antiqua"
585 size="5"><a name="_toc381201090">important colors field</a></p>
586 </font></b><font face="arial" size="3"><p align="justify">the <i>important colors</i>
587 field s</font><font face="book antiqua" size="3">pecifies the number of color indices that
588 are considered important for displaying the bitmap. if this value is zero, all colors are
589 important. </font></td>
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