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32 <body>
33 <main role="main">
34 <h1>GIF Metadata Format Specification</h1>
35 <a id="gif_stream_metadata_format"></a>
36 <h2>GIF Stream Metadata Format Specification</h2>
37
38 <p>
39
40 The GIF stream metadata format encodes the information stored in the
41 per-file header, namely the file version, logical screen descriptor,
42 and the global color table.
43
44 <p>
45
46 The logical screen descriptor describes the overall width and height
47 of an animated file, as well as information about the color resolution
48 (number of bits per pixel) and pixel aspect ratio.
49
50 <p>
51
52 The global color table contains a color lookup table that is used for
53 images that do not have their own local color table.
54
55 <pre>
56 <!DOCTYPE "javax_imageio_gif_stream_1.0" [
57
58 <!ELEMENT "javax_imageio_gif_stream_1.0" (Version?,
59 LogicalScreenDescriptor?, GlobalColorTable?)>
60
61 <!ELEMENT "Version" EMPTY>
62 <!-- The file version, either 87a or 89a -->
63 <!ATTLIST "Version" "value" ("87a" | "89a") #REQUIRED>
64 <!-- The version string -->
65
66 <!ELEMENT "LogicalScreenDescriptor" EMPTY>
67 <!-- The logical screen descriptor, except for the global color table -->
68 <!ATTLIST "LogicalScreenDescriptor" "logicalScreenWidth" #CDATA
69 #REQUIRED>
70 <!-- The width in pixels of the whole picture -->
71 <!-- Data type: Integer -->
72 <!-- Min value: 1 (inclusive) -->
73 <!-- Max value: 65535 (inclusive) -->
74 <!ATTLIST "LogicalScreenDescriptor" "logicalScreenHeight" #CDATA
75 #REQUIRED>
76 <!-- The height in pixels of the whole picture -->
77 <!-- Data type: Integer -->
78 <!-- Min value: 1 (inclusive) -->
79 <!-- Max value: 65535 (inclusive) -->
80 <!ATTLIST "LogicalScreenDescriptor" "colorResolution" #CDATA
81 #REQUIRED>
82 <!-- The number of bits of color resolution, beteen 1 and 8 -->
83 <!-- Data type: Integer -->
84 <!-- Min value: 1 (inclusive) -->
85 <!-- Max value: 8 (inclusive) -->
86 <!ATTLIST "LogicalScreenDescriptor" "pixelAspectRatio" #CDATA
87 #REQUIRED>
88 <!-- If 0, indicates square pixels, else W/H = (value + 15)/64 -->
89 <!-- Data type: Integer -->
90 <!-- Min value: 0 (inclusive) -->
91 <!-- Max value: 255 (inclusive) -->
92
93 <!ELEMENT "GlobalColorTable" (ColorTableEntry)*>
94 <!-- The global color table -->
95 <!-- Min children: 2 -->
96 <!-- Max children: 256 -->
97 <!ATTLIST "GlobalColorTable" "sizeOfGlobalColorTable" ("2" |
98 "4" | "8" | "16" | "32" | "64" | "128" | "256") #REQUIRED>
99 <!-- The number of entries in the global color table -->
100 <!ATTLIST "GlobalColorTable" "backgroundColorIndex" #CDATA
101 #REQUIRED>
102 <!-- The index of the color table entry to be used as a background -->
103 <!-- Data type: Integer -->
104 <!-- Min value: 0 (inclusive) -->
105 <!-- Max value: 255 (inclusive) -->
106 <!ATTLIST "GlobalColorTable" "sortFlag" ("TRUE" | "FALSE")
107 #REQUIRED>
108 <!-- True if the global color table is sorted by frequency -->
109
110 <!ELEMENT "ColorTableEntry" EMPTY>
111 <!-- A global color table entry -->
112 <!ATTLIST "ColorTableEntry" "index" #CDATA #REQUIRED>
113 <!-- The index of the color table entry -->
114 <!-- Data type: Integer -->
115 <!-- Min value: 0 (inclusive) -->
116 <!-- Max value: 255 (inclusive) -->
117 <!ATTLIST "ColorTableEntry" "red" #CDATA #REQUIRED>
118 <!-- The red value for the color table entry -->
119 <!-- Data type: Integer -->
120 <!-- Min value: 0 (inclusive) -->
121 <!-- Max value: 255 (inclusive) -->
122 <!ATTLIST "ColorTableEntry" "green" #CDATA #REQUIRED>
123 <!-- The green value for the color table entry -->
124 <!-- Data type: Integer -->
125 <!-- Min value: 0 (inclusive) -->
126 <!-- Max value: 255 (inclusive) -->
127 <!ATTLIST "ColorTableEntry" "blue" #CDATA #REQUIRED>
128 <!-- The blue value for the color table entry -->
129 <!-- Data type: Integer -->
130 <!-- Min value: 0 (inclusive) -->
131 <!-- Max value: 255 (inclusive) -->
132 ]>
133 </pre>
134 <a id="gif_image_metadata_format"></a>
135 <h2>GIF Image Metadata Format Specification</h2>
136 <p>
137
138 The GIF image metadata format encodes the image descriptor, local
139 color table, and extension information assciated with a single image
140 within a GIF file, typically a frame of an animation.
141
142 <p>
143
144 The image description contains the offset of the frame within the
145 logical screen described in the stream metadata, as well as the width
146 and height of the frame and whether it is used interlaced encoding.
147
148 <p>
149
150 The local color table, if present, supersedes the global color table
151 for the frame at hand.
152
153 <p>
154
155 The graphic control extension contains information on how the frame is
156 to be incorporated into the animation. The disposal method indicates
157 whether the current frame should remain in place
158 (<code>doNotDispose</code>), be restored to the backgound color as
159 specified in the stream metadata
160 (<code>restoreToBackgroundColor</code>), or be restored to the
161 previous frame contents (<code>restoreToPrevious</code>) prior to
162 displaying the subsequent frame.
163
164 <p>
165
166 The user input flag indicates whether the animation should pause for
167 user input before advancing to the next frame. The transparent color
168 flag and index indicate a color index for which pixels of the frame
169 should not be drawn. The delay time indicates how long the frame
170 should be displayed, in hundredths of a second. If the user input
171 flag is set and the delay time is 0, the frame is intended to be
172 advanced only on user input.
173
174 <pre>
175 <!DOCTYPE "javax_imageio_gif_image_1.0" [
176
177 <!ELEMENT "javax_imageio_gif_image_1.0" (ImageDescriptor?,
178 LocalColorTable?, GraphicControlExtension?, PlainTextExtension?,
179 ApplicationExtensions?, CommentExtensions?)>
180
181 <!ELEMENT "ImageDescriptor" EMPTY>
182 <!-- The image descriptor -->
183 <!ATTLIST "ImageDescriptor" "imageLeftPosition" #CDATA #REQUIRED>
184 <!-- The X offset of the image relative to the screen origin -->
185 <!-- Data type: Integer -->
186 <!-- Min value: 0 (inclusive) -->
187 <!-- Max value: 65535 (inclusive) -->
188 <!ATTLIST "ImageDescriptor" "imageTopPosition" #CDATA #REQUIRED>
189 <!-- The Y offset of the image relative to the screen origin -->
190 <!-- Data type: Integer -->
191 <!-- Min value: 0 (inclusive) -->
192 <!-- Max value: 65535 (inclusive) -->
193 <!ATTLIST "ImageDescriptor" "imageWidth" #CDATA #REQUIRED>
194 <!-- The width of the image -->
195 <!-- Data type: Integer -->
196 <!-- Min value: 1 (inclusive) -->
197 <!-- Max value: 65535 (inclusive) -->
198 <!ATTLIST "ImageDescriptor" "imageHeight" #CDATA #REQUIRED>
199 <!-- The height of the image -->
200 <!-- Data type: Integer -->
201 <!-- Min value: 1 (inclusive) -->
202 <!-- Max value: 65535 (inclusive) -->
203 <!ATTLIST "ImageDescriptor" "interlaceFlag" ("TRUE" | "FALSE")
204 #REQUIRED>
205 <!-- True if the image is stored using interlacing -->
206
207 <!ELEMENT "LocalColorTable" (ColorTableEntry)*>
208 <!-- The local color table -->
209 <!-- Min children: 2 -->
210 <!-- Max children: 256 -->
211 <!ATTLIST "LocalColorTable" "sizeOfLocalColorTable" ("2" |
212 "4" | "8" | "16" | "32" | "64" | "128" | "256") #REQUIRED>
213 <!-- The number of entries in the local color table -->
214 <!ATTLIST "LocalColorTable" "sortFlag" ("TRUE" | "FALSE")
215 #REQUIRED>
216 <!-- True if the local color table is sorted by frequency -->
217
218 <!ELEMENT "ColorTableEntry" EMPTY>
219 <!-- A local color table entry -->
220 <!ATTLIST "ColorTableEntry" "index" #CDATA #REQUIRED>
221 <!-- The index of the color table entry -->
222 <!-- Data type: Integer -->
223 <!-- Min value: 0 (inclusive) -->
224 <!-- Max value: 255 (inclusive) -->
225 <!ATTLIST "ColorTableEntry" "red" #CDATA #REQUIRED>
226 <!-- The red value for the color table entry -->
227 <!-- Data type: Integer -->
228 <!-- Min value: 0 (inclusive) -->
229 <!-- Max value: 255 (inclusive) -->
230 <!ATTLIST "ColorTableEntry" "green" #CDATA #REQUIRED>
231 <!-- The green value for the color table entry -->
232 <!-- Data type: Integer -->
233 <!-- Min value: 0 (inclusive) -->
234 <!-- Max value: 255 (inclusive) -->
235 <!ATTLIST "ColorTableEntry" "blue" #CDATA #REQUIRED>
236 <!-- The blue value for the color table entry -->
237 <!-- Data type: Integer -->
238 <!-- Min value: 0 (inclusive) -->
239 <!-- Max value: 255 (inclusive) -->
240
241 <!ELEMENT "GraphicControlExtension" EMPTY>
242 <!-- A graphic control extension -->
243 <!ATTLIST "GraphicControlExtension" "disposalMethod" ("none" |
244 "doNotDispose" | "restoreToBackgroundColor" |
245 "restoreToPrevious" | "undefinedDisposalMethod4" |
246 "undefinedDisposalMethod5" | "undefinedDisposalMethod6" |
247 "undefinedDisposalMethod7") #REQUIRED>
248 <!-- The disposal method for this frame -->
249 <!ATTLIST "GraphicControlExtension" "userInputFlag" ("TRUE" |
250 "FALSE") #REQUIRED>
251 <!-- True if the frame should be advanced based on user input -->
252 <!ATTLIST "GraphicControlExtension" "transparentColorFlag" (
253 "TRUE" | "FALSE") #REQUIRED>
254 <!-- True if a transparent color exists -->
255 <!ATTLIST "GraphicControlExtension" "delayTime" #CDATA #REQUIRED>
256 <!-- The time to delay between frames, in hundredths of a second -->
257 <!-- Data type: Integer -->
258 <!-- Min value: 0 (inclusive) -->
259 <!-- Max value: 65535 (inclusive) -->
260 <!ATTLIST "GraphicControlExtension" "transparentColorIndex"
261 #CDATA #REQUIRED>
262 <!-- The transparent color, if transparentColorFlag is true -->
263 <!-- Data type: Integer -->
264 <!-- Min value: 0 (inclusive) -->
265 <!-- Max value: 255 (inclusive) -->
266
267 <!ELEMENT "PlainTextExtension" EMPTY>
268 <!-- A plain text (text grid) extension -->
269 <!ATTLIST "PlainTextExtension" "textGridLeft" #CDATA #REQUIRED>
270 <!-- The X offset of the text grid -->
271 <!-- Data type: Integer -->
272 <!-- Min value: 0 (inclusive) -->
273 <!-- Max value: 65535 (inclusive) -->
274 <!ATTLIST "PlainTextExtension" "textGridTop" #CDATA #REQUIRED>
275 <!-- The Y offset of the text grid -->
276 <!-- Data type: Integer -->
277 <!-- Min value: 0 (inclusive) -->
278 <!-- Max value: 65535 (inclusive) -->
279 <!ATTLIST "PlainTextExtension" "textGridWidth" #CDATA #REQUIRED>
280 <!-- The number of columns in the text grid -->
281 <!-- Data type: Integer -->
282 <!-- Min value: 1 (inclusive) -->
283 <!-- Max value: 65535 (inclusive) -->
284 <!ATTLIST "PlainTextExtension" "textGridHeight" #CDATA #REQUIRED>
285 <!-- The number of rows in the text grid -->
286 <!-- Data type: Integer -->
287 <!-- Min value: 1 (inclusive) -->
288 <!-- Max value: 65535 (inclusive) -->
289 <!ATTLIST "PlainTextExtension" "characterCellWidth" #CDATA
290 #REQUIRED>
291 <!-- The width of a character cell -->
292 <!-- Data type: Integer -->
293 <!-- Min value: 1 (inclusive) -->
294 <!-- Max value: 255 (inclusive) -->
295 <!ATTLIST "PlainTextExtension" "characterCellHeight" #CDATA
296 #REQUIRED>
297 <!-- The height of a character cell -->
298 <!-- Data type: Integer -->
299 <!-- Min value: 1 (inclusive) -->
300 <!-- Max value: 255 (inclusive) -->
301 <!ATTLIST "PlainTextExtension" "textForegroundColor" #CDATA
302 #REQUIRED>
303 <!-- The text foreground color index -->
304 <!-- Data type: Integer -->
305 <!-- Min value: 0 (inclusive) -->
306 <!-- Max value: 255 (inclusive) -->
307 <!ATTLIST "PlainTextExtension" "textBackgroundColor" #CDATA
308 #REQUIRED>
309 <!-- The text background color index -->
310 <!-- Data type: Integer -->
311 <!-- Min value: 0 (inclusive) -->
312 <!-- Max value: 255 (inclusive) -->
313
314 <!ELEMENT "ApplicationExtensions" (ApplicationExtension)*>
315 <!-- A set of application extensions -->
316 <!-- Min children: 1 -->
317 <!-- Max children: 2147483647 -->
318
319 <!ELEMENT "ApplicationExtension" EMPTY>
320 <!-- An application extension -->
321 <!-- User object: array of byte -->
322 <!-- Min length: 0 -->
323 <!-- Max length: 2147483647 -->
324 <!ATTLIST "ApplicationExtension" "applicationID" #CDATA
325 #REQUIRED>
326 <!-- The application ID -->
327 <!-- Data type: String -->
328 <!ATTLIST "ApplicationExtension" "authenticationCode" #CDATA
329 #REQUIRED>
330 <!-- The authentication code -->
331 <!-- Data type: String -->
332
333 <!ELEMENT "CommentExtensions" (CommentExtension)*>
334 <!-- A set of comments -->
335 <!-- Min children: 1 -->
336 <!-- Max children: 2147483647 -->
337
338 <!ELEMENT "CommentExtension" EMPTY>
339 <!-- A comment -->
340 <!ATTLIST "CommentExtension" "value" #CDATA #REQUIRED>
341 <!-- The comment -->
342 <!-- Data type: String -->
343 ]>
344 </pre>
345
346 <p>
347 <a id="mapping"></a>
348 <table border=1>
349 <caption><b>Mapping of Standard to GIF Native Stream Metadata</b></caption>
350 <thead>
351 <tr>
352 <th scope="col">Index</th>
353 <th scope="col">Standard Metadata Component</th>
354 <th scope="col">GIF Native Stream Metadata Component</th>
355 </tr>
356 </thead>
357 <tbody>
358 <tr>
359 <th scope="row">1</th>
360 <td>/Chroma/Palette/PaletteEntry@index</td>
361 <td>/GlobalColorTable/ColorTableEntry@index</td>
362 </tr>
363 <tr>
364 <th scope="row">2</th>
365 <td>/Chroma/Palette/PaletteEntry@red</td>
366 <td>/GlobalColorTable/ColorTableEntry@red</td>
367 </tr>
368 <tr>
369 <th scope="row">3</th>
370 <td>/Chroma/Palette/PaletteEntry@green</td>
371 <td>/GlobalColorTable/ColorTableEntry@green</td>
372 </tr>
373 <tr>
374 <th scope="row">4</th>
375 <td>/Chroma/Palette/PaletteEntry@blue</td>
376 <td>/GlobalColorTable/ColorTableEntry@blue</td>
377 </tr>
378 <tr>
379 <th scope="row">5</th>
380 <td>/Chroma/BackgroundIndex@value</td>
381 <td>/GlobalColorTable@backgroundColorIndex</td>
382 </tr>
383 <tr>
384 <th scope="row">6</th>
385 <td>/Data/BitsPerSample@value</td>
386 <td>/LogicalScreenDescriptor@colorResolution</td>
387 </tr>
388 <tr>
389 <th scope="row">7</th>
390 <td>/Dimension/PixelAspectRatio@value</td>
391 <td>/LogicalScreenDescriptor@pixelAspectRatio</td>
392 </tr>
393 <tr>
394 <th scope="row">8</th>
395 <td>/Dimension/HorizontalScreenSize@value</td>
396 <td>/LogicalScreenDescriptor@logicalScreenWidth</td>
397 </tr>
398 <tr>
399 <th scope="row">9</th>
400 <td>/Dimension/VerticalScreenSize@value</td>
401 <td>/LogicalScreenDescriptor@logicalScreenHeight</td>
402 </tr>
403 <tr>
404 <th scope="row">10</th>
405 <td>/Document/FormatVersion@value</td>
406 <td>/Version@value</td>
407 </tr>
408 </tbody>
409 </table>
410
411 <table border=1>
412 <caption><b>Mapping of Standard to GIF Native Image Metadata</b></caption>
413 <thead>
414 <tr>
415 <th scope="col">Index</th>
416 <th scope="col">Standard Metadata Component</th>
417 <th scope="col">GIF Native Image Metadata Component</th>
418 </tr>
419 </thead>
420 <tbody>
421 <tr>
422 <th scope="row">1</th>
423 <td>/Chroma/Palette/PaletteEntry@index</td>
424 <td>/LocalColorTable/ColorTableEntry@index</td>
425 </tr>
426 <tr>
427 <th scope="row">2</th>
428 <td>/Chroma/Palette/PaletteEntry@red</td>
429 <td>/LocalColorTable/ColorTableEntry@red</td>
430 </tr>
431 <tr>
432 <th scope="row">3</th>
433 <td>/Chroma/Palette/PaletteEntry@green</td>
434 <td>/LocalColorTable/ColorTableEntry@green</td>
435 </tr>
436 <tr>
437 <th scope="row">4</th>
438 <td>/Chroma/Palette/PaletteEntry@blue</td>
439 <td>/LocalColorTable/ColorTableEntry@blue</td>
440 </tr>
441 <tr>
442 <th scope="row">5</th>
443 <td>/Dimension/HorizontalPixelOffset@value</td>
444 <td>/ImageDescriptor@imageLeftPosition</td>
445 </tr>
446 <tr>
447 <th scope="row">6</th>
448 <td>/Dimension/VerticalPixelOffset@value</td>
449 <td>/ImageDescriptor@imageTopPosition</td>
450 </tr>
451 <tr>
452 <th scope="row">7</th>
453 <td>/Text/TextEntry@value</td>
454 <td>/CommentExtensions/CommentExtension@value</td>
455 </tr>
456 <tr>
457 <th scope="row">8</th>
458 <td>/Transparency/TransparentIndex@value</td>
459 <td>/GraphicControlExtension@transparentColorIndex
460 (/GraphicControlExtension@transparentColorFlag is also set to
461 "TRUE")</td>
462 </tr>
463 </tbody>
464 </table>
465 </main>
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467 </html>