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35 <h1>JPEG Metadata Format Specification and Usage Notes</h1>
36
37 <p>
38 <a href=#metadata>JPEG Metadata</a><br>
39 <a href=#abbrev>Abbreviated Streams</a><br>
40 <a href=#tables>Sources of Tables</a><br>
41 <a href=#color>Colorspace Transformations and Conventional Markers</a><br>
42 <a href=#thumbs>Thumbnail Images</a><br>
43 <a href=#prog>Progressive Encoding</a><br>
44 <a href=#tree>Native Metadata Format Tree Structure and Editing</a><br>
45 <a href=#image>Image Metadata DTD</a><br>
46 <a href=#stream>Stream Metadata DTD</a>
47 <p>
48 <b>NOTE</b>: It is important to call <code>dispose()</code>
49 on the JPEG reader and writer objects when they are no longer needed, as
50 they consume significant native resources which are not adequately recovered
51 by garbage collection. Both reader and writer call <code>dispose()</code>
52 in their finalizers, but those finalizers may not be called before the native
53 code has exhausted native memory.
54
55 <p>
56
57 The JPEG writer does not support replacing pixels.
58
59 <h2>
60 <a id=metadata>JPEG Metadata</a>
61 </h2>
62 JPEG metadata consists of the data contained in marker segments in a JPEG
63 stream. The image metadata object returned from a read describes the
64 contents of the marker segments between the <code>SOI</code> marker and
65 the <code>EOI</code> marker for that image. The image metadata object
66 passed into a write determines the contents of the stream between the
67 <code>SOI</code> marker and the <code>EOI</code> marker for that image,
68 subject to the controls in any <code>ImageWriteParam</code>.
69
70 <p>
71 Stream metadata is used only for tables-only images found (or to be
72 placed) at the beginning of a stream containing abbreviated images.
73 Tables-only images are not treated as images and do not consume an
74 image index. The stream metadata object returned from a read describes the
75 contents of the marker segments between the <code>SOI</code> marker and
76 the <code>EOI</code> marker for the single tables-only image at the
77 beginning of the stream, if one is present. If no tables-only image is
78 present at the front of the stream, the <code>getStreamMetadata</code>
79 method of <code>ImageReader</code> returns <code>null</code>. If
80 stream metadata is provided to the writer, a single tables-only image
81 containing the tables from the stream metadata object will be written at
82 the beginning of the stream. If the stream metadata object contains no
83 tables, default tables will be written. As the sole purpose of stream
84 metadata is for specifying tables-only images at the front of abbreviated
85 streams, the stream metadata argument is useful only on the
86 <code>ImageWriter.prepareWriteSequence</code> method. It is ignored on all
87 other methods.
88
89 <p>
90 The <code>ImageWriter.getDefaultStreamMetadata</code> method returns an
91 object containing the tables from the <code>ImageWriteParam</code> argument,
92 if it is a <code>JPEGImageWriteParam</code> and contains tables. Otherwise,
93 the returned object will contain default tables.
94
95 <p>The <code>ImageWriter.getDefaultImageMetadata</code> method returns a
96 metadata object containing <b>no</b> tables if the
97 <code>ImageWriteParam</code> argument contains tables. Otherwise the
98 returned metadata object will contain default visually lossless tables.
99 Of course, only a <code>JPEGImageWriteParam</code> may contain tables.
100
101 <p>
102 If <code>ignoreMetadata</code> is set to <code>true</code> when the input
103 is set on the reader, stream metadata will not be available, but image
104 metadata will.
105
106 <h2>
107 <a id=abbrev>Abbreviated Streams</a>
108 </h2>
109 Both the reader and the writer retain their tables from one operation to the
110 next, thus permitting the use of abbreviated streams quite naturally, with a
111 few minor restrictions:
112 <ol>
113 <li> Abbreviated streams may contain only one tables-only image, which must
114 come first in the stream. Subsequent tables-only images will cause
115 undefined behavior.</li>
116 <li> Abbreviated streams must be read fully and in order. No random access
117 is allowed, in either direction. The same image may be read multiple
118 times. If a call is made with an image index that is not the same as
119 or one greater than the most recent call (or 0 if no calls have been
120 made), then an <code>IllegalArgumentException</code> is thrown.</li>
121 </ol>
122 These restrictions mean that streams may contain abbreviated images
123 interspersed with images containing tables. As required by JPEG, any tables
124 appearing in the stream override previous tables, regardless of the source
125 of the previous tables.
126
127 <p>
128 Note that once a tables-only image has been read, it's contents is available
129 as stream metadata from the reader until either another tables-only image
130 is read from another stream or the reader is reset. Changing the input does
131 not reset the stream metadata. This is useful for reading the tables from
132 one file, then changing the input to read an abbreviated stream containing
133 a sequence of images. The tables will be used automatically, and will remain
134 available as "stream" metadata.
135
136 <p>
137 Abbreviated streams are written using the sequence methods of
138 <code>ImageWriter</code>. Stream metadata is used to write a tables-only
139 image at the beginning of the stream, and the tables are set up for use, using
140 <code>ImageWriter.prepareWriteSequence</code>. If no stream metadata is
141 supplied to <code>ImageWriter.prepareWriteSequence</code>, then no
142 tables-only image is written. If stream metadata containing no tables is
143 supplied to <code>ImageWriter.prepareWriteSequence</code>, then a tables-only
144 image containing default visually lossless tables is written.
145
146 <h2>
147 <a id=tables>Sources of Tables</a>
148 </h2>
149 <p>
150 Images are written with tables if tables are present in their metadata objects
151 or without them if no tables are present in their metadata objects. If no
152 metadata object is present then the tables are written. The tables used for
153 compression are taken from one of the following sources, which are consulted
154 in order:
155 <ol>
156 <li> If there is an <code>ImageWriteParam</code> and the compression mode is
157 set to <code>EXPLICIT</code>, default tables constructed using the
158 quality setting are used. They are written only if the metadata
159 contains tables or if there is no metadata, but they replace the
160 tables in the metadata.</li>
161 <li> If there is an <code>ImageWriteParam</code> and the compression mode is
162 set to <code>DEFAULT</code>, default visually lossles tables are used.
163 They are written only if the metadata contains tables or if
164 there is no metadata, but they replace the tables in the
165 metadata.</li>
166 <li> Otherwise the compression mode on the <code>ImageWriteParam</code> must
167 be MODE_COPY_FROM_<code>METADATA</code>, in which case the following
168 are used:
169 <ol>
170 <li> the tables in the image metadata, if present</li>
171 <li> the tables in the stream metadata, if present</li>
172 <li> the tables in the <code>JPEGImageWriteParam</code>, if present</li>
173 <li> default visually lossless tables</li>
174 </ol> Tables are written only if they are taken from image metadata.
175 </li>
176 </ol>
177
178 This ordering implements the design intention that tables should be included
179 in <code>JPEGImageWriteParam</code>s only as a means of specifying tables
180 when no other source is available, and this can occur only when writing to an
181 abbreviated stream without tables using known non-standard tables for
182 compression.
183
184 <p>
185 When reading, tables in a <code>JPEGImageReadParam</code> are consulted only
186 if tables have not been set by any previous read. Tables set from a
187 <code>JPEGImageReadParam</code> are overridden by any tables present in the
188 stream being read.
189
190 <p>
191 Note that if no image metadata object is specified for a particular image, a
192 default object is used, which includes default tables.
193
194 <h2>
195 <a id=color>Colorspace Transformations and Conventional Markers</a>
196 </h2>
197 Colorspace transformations are controlled by the destination type for
198 both reading and writing of images. When <code>Raster</code>s are
199 read, no colorspace transformation is performed, and any destination type
200 is ignored. A warning is sent to any listeners if a destination type is
201 specified in this case. When <code>Raster</code>s are written, any
202 destination type is used to interpret the bands. This might result in a
203 JFIF or Adobe header being written, or different component ids being written
204 to the frame and scan headers. If values present in a metadata object do not
205 match the destination type, the destination type is used and a warning is sent
206 to any listeners.
207
208 <p>
209
210 <a id=optcolor><b>Optional ColorSpace support:</b></a>
211 Handling of PhotoYCC (YCC), PhotoYCCA (YCCA), RGBA and YCbCrA color spaces
212 by the standard plugin, as described below, is dependent on capabilities
213 of the libraries used to interpret the JPEG data. Thus all consequential
214 behaviors are optional. If the support is not available when decoding,
215 the color space will be treated as unrecognized and the appropriate
216 default color space for the specified number of component channels
217 may be used.
218 When writing, an Exception may be thrown if no suitable conversion
219 can be applied before encoding.
220 But where the support for these color spaces is available, the behavior
221 must be as documented.
222 <p>
223
224 When reading, the contents of the stream are interpreted by the usual
225 JPEG conventions, as follows:
226
227 <ul>
228 <li> If a JFIF <code>APP0</code> marker segment is present, the colorspace
229 is known to be either grayscale or YCbCr. If an <code>APP2</code>
230 marker segment containing an embedded ICC profile is also present, then
231 the YCbCr is converted to RGB according to the formulas given in the
232 JFIF spec, and the ICC profile is assumed to refer to the resulting RGB
233 space.
234 <li> If an Adobe <code>APP14</code> marker segment is present, the
235 colorspace is determined by consulting the <code>transform</code> flag.
236 The <code>transform</code> flag takes one of three values:
237 <ul>
238 <li> 2 - The image is encoded as YCCK (implicitly converted from
239 CMYK on encoding).
240
241 <li> 1 - The image is encoded as YCbCr (implicitly converted from RGB
242 on encoding).
243
244 <li> 0 - Unknown. 3-channel images are assumed to be RGB, 4-channel
245 images are assumed to be CMYK.
246 </ul>
247 <li> If neither marker segment is present, the following procedure is
248 followed: Single-channel images are assumed to be grayscale, and
249 2-channel images are assumed to be grayscale with an alpha channel.
250 For 3- and 4-channel images, the component ids are consulted. If these
251 values are 1-3 for a 3-channel image, then the image is assumed to be
252 YCbCr. Subject to the availability of the
253 <a href=#optcolor>optional color space support</a>
254 described above, if these values are 1-4 for a 4-channel image,
255 then the image is assumed to be YCbCrA.
256 If these values are > 4, they are checked
257 against the ASCII codes for 'R', 'G', 'B', 'A', 'C', 'c'. These can
258 encode the following colorspaces:
259 <p>
260 <br>RGB
261 <br>RGBA
262 <br>YCC (as 'Y','C','c'), assumed to be PhotoYCC
263 <br>YCCA (as 'Y','C','c','A'), assumed to be PhotoYCCA
264 <p>
265 Otherwise, 3-channel subsampled images are assumed to be YCbCr,
266 3-channel non-subsampled images are assumed to be RGB, 4-channel
267 subsampled images are assumed to be YCCK, and 4-channel, non-subsampled
268 images are assumed to be CMYK.
269
270 <li> All other images are declared uninterpretable and an exception is
271 thrown if an attempt is made to read one as a
272 <code>BufferedImage</code>. Such an image may be read only as a
273 <code>Raster</code>. If an image is interpretable but there is no Java
274 <code>ColorSpace</code> available corresponding to the encoded
275 colorspace (<i>e.g.</i> YCbCr), then
276 <code>ImageReader.getRawImageType</code> will return <code>null</code>.
277 </ul>
278
279 Once an encoded colorspace is determined, then the target colorspace is
280 determined as follows:
281
282 <ul>
283 <li> If a destination type is not set, then the following default
284 transformations take place after upsampling: YCbCr (and YCbCrA) images
285 are converted to RGB (and RGBA) using the conversion provided by the
286 underlying IJG library and either the built-in sRGB
287 <code>ColorSpace</code> or a custom RGB <code>ColorSpace</code> object
288 based on an embedded ICC profile is used to create the output
289 <code>ColorModel</code>. PhotoYCC and PhotoYCCA images are not
290 converted. CMYK and YCCK images are currently not supported.</li>
291
292 <li> If a destination image or type is set, it is used as follows:
293 If the IJG library provides an appropriate conversion, it is used.
294 Otherwise the default library conversion is followed by a colorspace
295 conversion in Java.</li>
296
297 <li> Bands are selected AFTER any library colorspace conversion. If a
298 subset of either source or destination bands is used, then the default
299 library conversions are used with no further conversion in Java,
300 regardless of any destination type.</li>
301
302 <li> An exception is thrown if an attempt is made to read an image in an
303 unsupported jpeg colorspace as a <code>BufferedImage</code>
304 (<i>e.g.</i> CMYK). Such images may be read as
305 <code>Raster</code>s. If an image colorspace is unsupported or
306 uninterpretable, then <code>ImageReader.getImageTypes</code> will
307 return an empty <code>Iterator</code>. If a subset of the raw bands
308 are required, a <code>Raster</code> must be obtained first and the
309 bands obtained from that. </li>
310 </ul>
311
312 <p>
313 For writing, the color transformation to apply is determined as
314 follows:
315
316 <p>
317 If a subset of the source bands is to be written, no color conversion is
318 performed. Any destination, if set, must match the number of bands that will
319 be written, and serves as an interpretation of the selected bands, rather than
320 a conversion request. This behavior is identical to that for
321 <code>Raster</code>s. If all the bands are to be written and an image
322 (as opposed to a <code>Raster</code>) is being written, any destination type
323 is ignored and a warning is sent to any listeners.
324
325 <p>
326 If a destination type is used and any aspect of the metadata object, if there
327 is one, is not compatible with that type, the destination type is used, the
328 metadata written is modified from that provided, and a warning is sent to
329 listeners. This includes the <code>app0JFIF</code> and
330 <code>app14Adobe</code> nodes. The component ids in the <code>sof</code> and
331 <code>sos</code> nodes are not modified, however, as unless a
332 <code>app0JFIF</code> node is present, any values may be used.
333 <p>
334
335 When a full image is written, a destination colorspace will be
336 chosen based on the image contents and the metadata settings, according to
337 the following algorithm:
338
339 <p>
340
341 If no metadata object is specified, then the following defaults apply:
342
343 <ul>
344 <li> Grayscale images are written with a JFIF <code>APP0</code> marker
345 segment. Grayscale images with alpha are written with no special
346 marker. As required by JFIF, the component ids in the frame and
347 scan header is set to 1.
348
349 <li> RGB images are converted to YCbCr, subsampled in the chrominance
350 channels by half both vertically and horizontally, and written with a
351 JFIF <code>APP0</code> marker segment. If the <code>ColorSpace</code>
352 of the image is based on an <code>ICCProfile</code> (it is an instance
353 of <code>ICC_ColorSpace</code>, but is not one of the standard built-in
354 <code>ColorSpaces</code>), then that profile is embedded in an
355 <code>APP2</code> marker segment. As required by JFIF, the
356 component ids in the frame and scan headers are set to 1, 2, and 3.
357
358
359 <li> Subject to the <a href=#optcolor>optional library support</a>
360 described above,
361 RGBA images are converted to YCbCrA, subsampled in the
362 chrominance channels by half both vertically and horizontally, and
363 written without any special marker segments. The component ids
364 in the frame and scan headers are set to 1, 2, 3, and 4.
365
366 <li> Subject to the <a href=#optcolor>optional library support</a>
367 described above,
368 PhotoYCC and YCCAimages are subsampled by half in the chrominance
369 channels both vertically and horizontally and written with an
370 Adobe <code>APP14</code> marker segment and 'Y','C', and 'c' (and
371 'A' if an alpha channel is present) as component ids in the frame
372 and scan headers.
373 </ul>
374
375 Default metadata objects for these image types will reflect these settings.
376
377 <p>
378
379 If a metadata object is specified, then the number of channels in the
380 frame and scan headers must always match the number of bands to be
381 written, or an exception is thrown. <code>app0JFIF</code> and
382 <code>app14Adobe</code> nodes may appear in the same metadata object only
383 if the <code>app14Adobe</code> node indicates YCbCr, and the component ids
384 are JFIF compatible (0-2). The various image types are processed in the
385 following ways:
386
387 <br>
388
389 (All multi-channel images are subsampled according to the sampling factors
390 in the frame header node of the metadata object, regardless of color space.)
391
392 <ul>
393 <li> Grayscale Images:
394 <ul>
395 <li> If an <code>app0JFIF</code> node is present in the metadata object,
396 a JFIF <code>APP0</code> marker segment is written.
397 <li> If an <code>app14Adobe</code> node is present in the metadata
398 object, it is checked for validity (<code>transform</code> must be
399 <code>UNKNOWN</code>) and written.
400 <li> If neither node is present in the metadata object, no special
401 marker segment is written.
402 </ul>
403
404 <li> Grayscale Images with an Alpha Channel:
405 <ul>
406 <li> If an <code>app0JFIF</code> node is present in the metadata object,
407 it is ignored and a warning is sent to listeners, as JFIF does not
408 support 2-channel images.
409 <li> If an <code>app14Adobe</code> node is present in the metadata
410 object, it is checked for validity (<code>transform</code> must be
411 <code>UNKNOWN</code>) and written. If <code>transform</code> is
412 not <code>UNKNOWN</code>, a warning is sent to listeners and the
413 correct transform is written.
414 <li> If neither node is present in the metadata object, no special
415 marker segment is written.
416 </ul>
417
418 <li> RGB Images:
419 <ul>
420 <li> If an <code>app0JFIF</code> node is present in the metadata object,
421 the image is converted to YCbCr and written with a JFIF
422 <code>APP0</code> marker segment. If the <code>ColorSpace</code>
423 of the image is based on a non-standard ICC Profile, then that
424 profile is embedded in an <code>APP2</code> marker segment. If the
425 <code>ColorSpace</code> is not based on a non-standard ICC Profile,
426 but an <code>app2ICC</code> node appears in the metadata, then an
427 <code>APP2</code> marker segment is written with the appropriate
428 standard profile. Note that the profile must specify an RGB color
429 space, as the file must be JFIF compliant.
430
431 <li> If an <code>app14Adobe</code> node is present in the metadata
432 object, the image is converted according to the color transform
433 setting and written with an Adobe <code>APP14</code> marker
434 segment. Component ids are written just as they appear in the
435 frame and scan headers. The color transform must be either YCbCr
436 or <code>UNKNOWN</code>. If it is <code>UNKNOWN</code>, the image
437 is not color converted.
438
439 <li> If neither node is present, the component ids in the frame
440 header are consulted. If these indicate a colorspace as described
441 above, then the image is converted to that colorspace if possible.
442 If the component ids do not indicate a colorspace, then the
443 sampling factors are consulted. If the image is to be subsampled,
444 it is converted to YCbCr first. If the image is not to be
445 subsampled, then no conversion is applied. No special marker
446 segmentss are written.
447 </ul>
448
449 <li> RGBA images:
450 Subject to the <a href=#optcolor>optional library support</a>
451 described above,
452 <ul>
453 <li> If an <code>app0JFIF</code> node is present in the metadata object,
454 it is ignored and a warning is sent to listeners, as JFIF does not
455 support 4-channel images.
456
457 <li> If an <code>app14Adobe</code> node is present in the metadata
458 object, the image is written with an Adobe <code>APP14</code> marker
459 segment. No colorspace conversion is performed. Component ids
460 are written just as they appear in the frame and scan headers.
461 The color transform must be <code>UNKNOWN</code>. If it is
462 not, a warning is sent to listeners.
463
464 <li> If no <code>app14Adobe</code> node is present, the component ids in
465 the frame header are consulted. If these indicate a colorspace as
466 described above, then the image is converted to that colorspace if
467 possible. If the component ids do not indicate a colorspace, then
468 the sampling factors are consulted. If the image is to be
469 subsampled, it is converted to YCbCrA. If the image is not to be
470 subsampled, then no conversion is applied. No special marker
471 segments are written.
472 </ul>
473
474 <li> PhotoYCC Images:
475 Subject to the <a href=#optcolor>optional library support</a>
476 described above,
477 <ul>
478 <li> If an <code>app0JFIF</code> node is present in the metadata object,
479 the image is converted to sRGB, and then to YCbCr during encoding,
480 and a JFIF <code>APP0</code> marker segment is written.
481
482 <li> If an <code>app14Adobe</code> node is present in the metadata
483 object, no conversion is applied, and an Adobe <code>APP14</code>
484 marker segment is written. The color transform must be YCC. If it
485 is not, a warning is sent to listeners.
486
487 <li> If neither node is present in the metadata object, no conversion
488 is applied, and no special marker segment is written.
489 </ul>
490
491 <li> PhotoYCCA Images:
492 Subject to the <a href=#optcolor>optional library support</a>
493 described above,
494 <ul>
495 <li> If an <code>app0JFIF</code> node is present in the metadata object,
496 it is ignored and a warning is sent to listeners, as JFIF does not
497 support 4-channel images.
498
499 <li> If an <code>app14Adobe</code> node is present in the metadata
500 object, no conversion is applied, and an Adobe <code>APP14</code>
501 marker segment is written. The color transform must be
502 <code>UNKNOWN</code>. If it is not, a warning is sent to
503 listeners.
504
505 <li> If neither node is present in the metadata object, no conversion
506 is applied, and no special marker segment is written.
507 </ul>
508 </ul>
509
510 <h2>
511 <a id=thumbs>Thumbnail Images</a>
512 </h2>
513 Thumbnails are supported by the use of JFIF and JFIF extension marker segments.
514 Thumbnails provided on the write methods determine the thumbnails that will be
515 included. <code>app0JFIF</code> and <code>app0JFXX</code> nodes present in
516 the metadata do not contain any thumbnail pixel data. However, the kinds of
517 thumbnails written depend on the contents of the metadata object, as follows.
518 Any thumbnail which is to be written as an indexed or RGB image and which is
519 larger than 255 by 255 will be clipped, not scaled, to 255 by 255. Thumbnails
520 written as JPEG images may be any size. A warning is sent to any listeners
521 whenever a thumbnail is clipped.
522 <ul>
523 <li> If there is a single thumbnail, it is processed as follows:
524 <ul>
525 <li> If the thumbnail image is an RGB palette image, it is processed as
526 follows:
527 <ul>
528 <li> If no <code>app0JFXX</code> node is present in the metadata, or
529 the first <code>app0JFXX</code> node present in the metadata
530 contains a <code>JFIFthumbPalette</code> element, a
531 palette thumbnail is written in a JFXX <code>APP0</code> marker
532 segment.
533 <li> If the first <code>app0JFXX</code> node present in the metadata
534 contains another thumbnail form (RGB or JPEG), the palette
535 image is expanded to RGB and the indicated thumbnail form is
536 written.
537 </ul>
538
539 <li> If the thumbnail image is an RGB image, it is processed as follows:
540 <ul>
541 <li> If no <code>app0JFXX</code> node is present in the metadata,
542 the thumbnail is written as part of the JFIF <code>APP0</code>
543 marker segment.
544 <li> If the first <code>app0JFXX</code> node present in the metadata
545 contains a <code>JFIFthumbRGB</code> element, an
546 RGB thumbnail is written in a JFXX <code>APP0</code> marker
547 segment.
548 <li> If the first <code>app0JFXX</code> node present in the metadata
549 contains a <code>JFIFthumbJPEG</code> element, a
550 JPEG thumbnail is written in a JFXX <code>APP0</code> marker
551 segment.
552 <li> If the first <code>app0JFXX</code> node present in the metadata
553 contains a <code>JFIFthumbPalette</code> element, an
554 RGB thumbnail is written in a JFXX <code>APP0</code> marker
555 segment and a warning is sent to any listeners.
556 </ul>
557
558 <li> If the thumbnail image is a grayscale image, it is processed as
559 follows:
560 <ul>
561 <li> If no <code>app0JFXX</code> node is present in the metadata,
562 the thumbnail is expanded to RGB and written as part of the
563 JFIF <code>APP0</code> marker segment.
564 <li> If the first <code>app0JFXX</code> node present in the metadata
565 contains a <code>JFIFthumbRGB</code> element, the thumbnail is
566 expanded to RGB and written in a separate <code>JFXX</code> RGB
567 marker segment.
568 <li> If the first <code>app0JFXX</code> node present in the metadata
569 contains a <code>JFIFthumbJPEG</code> element, a
570 JPEG thumbnail is written in a JFXX <code>APP0</code> marker
571 segment.
572 <li> If the first <code>app0JFXX</code> node present in the metadata
573 contains a <code>JFIFthumbPalette</code> element, a
574 JPEG thumbnail is written in a JFXX <code>APP0</code> marker
575 segment and a warning is sent to any listeners.
576 </ul>
577
578 <li> Any other thumbnail image types are ignored and a warning is sent
579 to any listeners.
580 </ul>
581
582 <li> If there are multiple thumbnails, each one is processed as above, except
583 that no thumbnail is placed in the JFIF <code>APP0</code> segment, and
584 the <code>app0JFXX</code> node consulted for each thumbnail is the
585 <code>app0JFXX</code> node from the metadata that occurs in the same
586 sequence as the thumbnail. <i>I.e.</i> the first
587 <code>app0JFXX</code> node applies to the first thumbnail, the second
588 node to the second thumbnail, and so on. If there are fewer
589 <code>app0JFXX</code> nodes in the metadata than thumbnails, then
590 those thumbnails are considered to have no matching
591 <code>app0JFXX</code> node. An RGB thumbnail with no matching
592 <code>app0JFXX</code> node is written in a JFXX <code>APP0</code> marker
593 segment. A grayscale thumbnail with no matching
594 <code>app0JFXX</code> node is written as a JPEG image to a JFXX
595 <code>APP0</code> marker segment.
596 </ul>
597 <p>
598
599 Note that as the only mechanism for storing thumbnails is via the
600 JFIF or JFIF extension marker segments, only grayscale or RGB images
601 may have thumbnails. If thumbnails are present when writing any other type
602 of image, the thumbnails are ignored and a warning is sent to any warning
603 listeners.
604
605 <h2>
606 <a id=prog>Progressive Encoding</a>
607 </h2>
608
609 Progressive encoding must be enabled on the <code>ImageWriteParam</code>
610 passed in to a write operation, or the image will be written sequentially,
611 regardless of the scan headers included in the metadata object. If
612 progressive encoding is enabled and set to copy from metadata, then
613 the sequence of scan headers from the metadata is used to write the
614 image. If progressive encoding is enabled and set to use a default,
615 then the scans in the metadata are ignored and a default set of scans
616 is used. Progressive encoding always forces optimized Huffman tables to
617 be used. Any Huffman tables present in the metadata will be ignored,
618 and a warning will be sent to any warning listeners.
619
620 If Huffman-table optimization is requested on the <code>ImageWriteParam</code>,
621 all Huffman tables in the metadata or in the <code>ImageWriteParam</code>
622 itself are ignored, and a warning will be sent to any warning listeners if
623 any such tables are present.
624
625 <h2>
626 <a id=tree>Native Metadata Format Tree Structure and Editing</a>
627 </h2>
628
629 The DTDs below describe just the trees of metadata objects actually returned
630 by the <code>IIOMetadata</code> object. They do not include nodes
631 corresponding to <code>SOI</code>, <code>EOI</code>, or <code>RST</code>
632 markers, as these parsing delimiters do not carry any meaningful metadata.
633 <p>
634
635 The first node is always a <code>JPEGvariety</code> node. In the
636 <code>javax_imageio_jpeg_image_1.0</code> version of the JPEG metadata
637 format, this node may have one child, an <code>app0JFIF</code> node,
638 indicating that the JPEG stream contains a JFIF marker segment and related
639 data, or no children, indicating that the stream contains no JFIF marker.
640 In future versions of the JPEG metadata format, other varieties of JPEG
641 metadata may be supported (e.g. Exif) by defining other types of nodes
642 which may appear as a child of the <code>JPEGvariety</code> node.
643 <p>
644
645 (Note that an application wishing to interpret Exif metadata given
646 a metadata tree structure in the <code>javax_imageio_jpeg_image_1.0</code>
647 format must check for an <code>unknown</code> marker segment with a tag
648 indicating an <code>APP1</code> marker and containing data identifying it
649 as an Exif marker segment. Then it may use application-specific code to
650 interpret the data in the marker segment. If such an application were
651 to encounter a metadata tree formatted according to a future version of
652 the JPEG metadata format, the Exif marker segment might not be
653 <code>unknown</code> in that format - it might be structured as a
654 child node of the <code>JPEGvariety</code> node. Thus, it is important
655 for an application to specify which version to use by passing the string
656 identifying the version to the method/constructor used to obtain an
657 <code>IIOMetadata</code> object.)
658
659 <p>
660
661 On reading, <code>JFXX</code> and <code>app2ICC</code> nodes occur as
662 children of an <code>app0JFIF</code> node.
663 This is true regardless of where the JFXX <code>APP0</code> and
664 <code>APP2</code> marker segments actually occur in the stream. The ordering
665 of nodes within the <code>markerSequence</code> node corresponds to the
666 ordering of marker segments found in the JPEG stream.
667 <p>
668 On writing, any <code>JFXX</code> and <code>app2ICC</code> nodes must
669 occur as children of an <code>app0JFIF</code> node, itself a child of a
670 <code>JPEGvariety</code> node, which must always be the first node.
671 (If the stream is not to be JFIF compliant, no <code>app0JFIF</code> node
672 should be provided, and the <code>JPEGvariety</code> node should have no
673 children.) Any
674 JFIF <code>APP0</code>, JFXX <code>APP0</code>, and <code>APP2</code> marker
675 segments are written first, followed by all Adobe <code>APP14</code>,
676 <code>APPn</code>, <code>COM</code> and unknown segments in the
677 order in which their corresponding nodes appear in the
678 <code>markerSequence</code> node, followed by <code>DQT</code> (and
679 <code>DHT</code> for non-progressive writes) marker segments, followed by the
680 <code>SOF</code> and <code>SOS</code> marker segments. For progressive writes
681 using metadata to control progression, the <code>SOS</code> segments are used
682 in the order in which their corresponding nodes occur in the
683 <code>markerSequence</code> node.
684 <p>
685
686 The <code>reset</code>, <code>mergeTree</code> and <code>setFromTree</code>
687 operations have the following semantics for the JPEG plug-in metadata object:
688
689 <p> <code>reset</code> - A call to <code>reset</code> will restore the
690 metadata object to the same state it had immediately after creation, whether
691 this came about from reading a stream or by obtaining a default object from
692 the <code>ImageWriter</code>. This is true regardless of how many times the
693 metadata object has been modified since creation.
694
695 <p> <code>mergeTree</code> - Native Format
696 <br> The <code>mergeTree</code> operation accepts valid trees conforming to
697 the DTD below, and merges the nodes using the following ordering rules. In
698 all cases, only data present in the new node is changed in a corresponding
699 existing node, if any. This means that nodes cannot be removed using
700 <code>mergeTree</code>. To remove nodes, use <code>setFromTree</code>. The
701 tree must consist of <code>IIOMetadataNode</code>s.
702 <ul>
703 <li> <code>app0JFIF</code>
704 <ul>
705 <li> If an <code>app0JFIF</code> node already exists, the contents
706 of the new one modify the existing one.
707 <li> If there is no such node, a new one is created and inserted in
708 the appropriate position.
709 </ul>
710 <li> <code>dqt</code>
711 <ul>
712 <li> If there already exist <code>dqt</code> nodes in the sequence,
713 then each table in the node replaces the first table, in any
714 <code>dqt</code> node, with the same table id.
715 <li> If none of the existing <code>dqt</code> nodes contain a table
716 with the same id, then the table is added to the last existing
717 <code>dqt</code> node.
718 <li> If there are no <code>dqt</code> nodes, then a new one is
719 created and added as follows:
720 <ul>
721 <li> If there are <code>dht</code> nodes, the new
722 <code>dqt</code> node is inserted before the first one.
723 <li> If there are no <code>dht</code> nodes, the new
724 <code>dqt</code> node is inserted before an
725 <code>sof</code> node, if there is one.
726 <li> If there is no <code>sof</code> node, the new
727 <code>dqt</code> node is inserted before the first
728 <code>sos</code> node, if there is one.
729 <li> If there is no <code>sos</code> node, the new
730 <code>dqt</code> node is added to the end of the sequence.
731 </ul>
732 </ul>
733 <li> <code>dht</code>
734 <ul>
735 <li> If there already exist <code>dht</code> nodes in the sequence,
736 then each table in the node replaces the first table, in any
737 <code>dht</code> node, with the same table class and table id.
738 <li> If none of the existing <code>dht</code> nodes contain a table
739 with the same class and id, then the table is added to the last
740 existing <code>dht</code> node.
741 <li> If there are no <code>dht</code> nodes, then a new one is
742 created and added as follows:
743 <ul>
744 <li> If there are <code>dqt</code> nodes, the new
745 <code>dht</code> node is inserted immediately following the
746 last <code>dqt</code> node.
747 <li> If there are no <code>dqt</code> nodes, the new
748 <code>dht</code> node is inserted before an
749 <code>sof</code> node, if there is one.
750 <li> If there is no <code>sof</code> node, the new
751 <code>dht</code> node is inserted before the first
752 <code>sos</code> node, if there is one.
753 <li> If there is no <code>sos</code> node, the new
754 <code>dht</code> node is added to the end of the sequence.
755 </ul>
756 </ul>
757 <li> <code>dri</code>
758 <ul>
759 <li> If there already exists a <code>dri</code> node, the restart
760 interval value is updated.
761 <li> If there is no <code>dri</code> node, then a new one is created
762 and added as follows:
763 <ul>
764 <li> If there is an <code>sof</code> node, the new
765 <code>dri</code> node is inserted before it.
766 <li> If there is no <code>sof</code> node, the new
767 <code>dri</code> node is inserted before the first
768 <code>sos</code> node, if there is one.
769 <li> If there is no <code>sos</code> node, the new
770 <code>dri</code> node is added to the end of the sequence.
771 </ul>
772 </ul>
773 <li> <code>com</code>
774 <br> A new <code>com</code> node is created and inserted as follows:
775 <ul>
776 <li> If there already exist <code>com</code> nodes, the new one is
777 inserted after the last one.
778 <li> If there are no <code>com</code> nodes, the new
779 <code>com</code> node is inserted after the
780 <code>app14Adobe</code> node, if there is one.
781 <li> If there is no <code>app14Adobe</code> node, the new
782 <code>com</code> node is inserted at the beginning of the
783 sequence.
784 </ul>
785 <li> <code>app14Adobe</code>
786 <ul>
787 <li> If there already exists an <code>app14Adobe</code> node, then
788 its attributes are updated from the node.
789 <li> If there is no <code>app14Adobe</code> node, then a new one is
790 created and added as follows:
791 <ul>
792 <li> The new <code>app14Adobe</code> node is inserted after the
793 last <code>unknown</code> node, if there are any.
794 <li> If there are no <code>unknown</code> nodes, the new
795 <code>app14Adobe</code> node is inserted at the beginning
796 of the sequence.
797 </ul>
798 </ul>
799 <li> <code>unknown</code>
800 <br> A new <code>unknown</code> node is created and added to the
801 sequence as follows:
802 <ul>
803 <li> If there already exist <code>unknown</code> marker nodes, the
804 new one is inserted after the last one.
805 <li> If there are no <code>unknown</code> nodes, the new
806 <code>unknown</code> node is inserted before the
807 <code>app14Adobe</code> node, if there is one.
808 <li> If there is no <code>app14Adobe</code> node, the new
809 <code>unknown</code> node is inserted at the beginning of the
810 sequence.
811 </ul>
812 <li> <code>sof</code>
813 <ul>
814 <li> If there already exists an <code>sof</code> node in the
815 sequence, then its values are updated from the node.
816 <li> If there is no <code>sof</code> node, then a new one is created
817 and added as follows:
818 <ul>
819 <li> If there are any <code>sos</code> nodes, the new
820 <code>sof</code> node is inserted before the first one.
821 <li> If there is no <code>sos</code> node, the new
822 <code>sof</code> node is added to the end of the sequence.
823 </ul>
824 </ul>
825 <li> <code>sos</code>
826 <ul>
827 <li> If there already exists a single <code>sos</code> node, then
828 the values are updated from the node.
829 <li> If there are more than one existing <code>sos</code> nodes,
830 then an <code>IIOInvalidTreeException</code> is thrown, as
831 <code>sos</code> nodes cannot be merged into a set of
832 progressive scans.
833 <li> If there are no <code>sos</code> nodes, a new one is created
834 and added to the end of the sequence.
835 </ul>
836 </ul>
837
838 <p> <code>mergeTree</code> - Standard Format
839 <br>
840 The <code>mergeTree</code> operation, when given a tree in the standard
841 format, will modify the native tree in the following ways:
842 <ul>
843 <li> <code>Chroma</code> - The <code>ColorSpaceType</code> subnode of a
844 <code>Chroma</code> node may change the target colorspace of the
845 compressed image. The selection of a new colorspace can cause a number
846 of changes, in keeping with the algorithms described above:
847 <code>app0JFIF</code> and <code>app14Adobe</code> nodes may be added
848 or removed, subsampling may be added or removed, component ids may
849 be changed, and <code>sof</code> and <code>sos</code> nodes will be
850 updated accordingly. If necessary, additional quantization and
851 huffman tables are added. In the case of quantization tables, the
852 default will be scaled to match the quality level of any existing
853 tables. No tables are added to metadata that does not already contain
854 tables. If the existing metadata specifies progressive encoding, then
855 the number of channels must not change. Any <code>Transparency</code>
856 node is also taken into account, as an explicit value of
857 <code>none</code> for the <code>Alpha</code> subnode can cause the
858 removal of an alpha channel, and anything other than <code>none</code>
859 can cause the addition of an alpha channel.
860 <li> <code>Dimension</code> - A <code>PixelAspectRatio</code> specification
861 can cause the contents of an <code>app0JFIF</code> node to change, if
862 there is one present, or the addition of an <code>app0JFIF</code> node
863 containing appropriate values, if there can be one. An appropriate
864 pair of integers is computed from the floating-point ratio for
865 inclusion in the node.
866 <li> <code>Text</code> - Each uncompressed text item is converted to a
867 <code>com</code> node and inserted according to the rules above for
868 merging <code>com</code> nodes.
869 </ul>
870
871 <p> <code>setFromTree</code> - Native Format
872 <br>
873 The <code>setFromTree</code> operation, when given a tree in the native
874 format described below, will simply replace the existing tree in its entirety
875 with the new one. The tree must consist of <code>IIOMetadataNode</code>s.
876
877 <p> <code>setFromTree</code> - Standard Format
878 <br>
879 The <code>setFromTree</code> operation, when given a tree in the standard
880 format, performs a <code>reset</code> followed by a merge of the new tree.
881
882 <h2>
883 <a id=image>Image Metadata DTD</a>
884 </h2>
885
886 <pre>
887 <!DOCTYPE "javax_imageio_jpeg_image_1.0" [
888
889 <!ELEMENT "javax_imageio_jpeg_image_1.0" (JPEGvariety, markerSequence)>
890
891 <!ELEMENT "JPEGvariety" (app0JFIF)>
892 <!-- A node grouping all marker segments specific to the variety of
893 stream being read/written (e.g. JFIF) - may be empty -->
894
895 <!ELEMENT "app0JFIF" (JFXX?, app2ICC?)>
896 <!ATTLIST "app0JFIF" "majorVersion" #CDATA "1">
897 <!-- The major JFIF version number -->
898 <!-- Data type: Integer -->
899 <!-- Min value: 0 (inclusive) -->
900 <!-- Max value: 255 (inclusive) -->
901 <!ATTLIST "app0JFIF" "minorVersion" #CDATA "2">
902 <!-- The minor JFIF version number -->
903 <!-- Data type: Integer -->
904 <!-- Min value: 0 (inclusive) -->
905 <!-- Max value: 255 (inclusive) -->
906 <!ATTLIST "app0JFIF" "resUnits" ("0" | "1" | "2") "0">
907 <!-- The resolution units for Xdensisty and Ydensity (0 = no
908 units, just aspect ratio; 1 = dots/inch; 2 = dots/cm) -->
909 <!ATTLIST "app0JFIF" "Xdensity" #CDATA "1">
910 <!-- The horizontal density or aspect ratio numerator -->
911 <!-- Data type: Integer -->
912 <!-- Min value: 1 (inclusive) -->
913 <!-- Max value: 65535 (inclusive) -->
914 <!ATTLIST "app0JFIF" "Ydensity" #CDATA "1">
915 <!-- The vertical density or aspect ratio denominator -->
916 <!-- Data type: Integer -->
917 <!-- Min value: 1 (inclusive) -->
918 <!-- Max value: 65535 (inclusive) -->
919 <!ATTLIST "app0JFIF" "thumbWidth" #CDATA "0">
920 <!-- The width of the thumbnail, or 0 if there isn't one -->
921 <!-- Data type: Integer -->
922 <!-- Min value: 0 (inclusive) -->
923 <!-- Max value: 255 (inclusive) -->
924 <!ATTLIST "app0JFIF" "thumbHeight" #CDATA "0">
925 <!-- The height of the thumbnail, or 0 if there isn't one -->
926 <!-- Data type: Integer -->
927 <!-- Min value: 0 (inclusive) -->
928 <!-- Max value: 255 (inclusive) -->
929
930 <!ELEMENT "JFXX" (app0JFXX)*>
931 <!-- Min children: 1 -->
932
933 <!ELEMENT "app0JFXX" (JFIFthumbJPEG | JFIFthumbPalette |
934 JFIFthumbRGB)>
935 <!-- A JFIF extension marker segment -->
936 <!ATTLIST "app0JFXX" "extensionCode" ("16" | "17" | "19")
937 #IMPLIED>
938 <!-- The JFXX extension code identifying thumbnail type: (16 =
939 JPEG, 17 = indexed, 19 = RGB -->
940
941 <!ELEMENT "JFIFthumbJPEG" (markerSequence?)>
942 <!-- A JFIF thumbnail in JPEG format (no JFIF segments
943 permitted) -->
944
945 <!ELEMENT "JFIFthumbPalette" EMPTY>
946 <!-- A JFIF thumbnail as an RGB indexed image -->
947 <!ATTLIST "JFIFthumbPalette" "thumbWidth" #CDATA #IMPLIED>
948 <!-- The width of the thumbnail -->
949 <!-- Data type: Integer -->
950 <!-- Min value: 0 (inclusive) -->
951 <!-- Max value: 255 (inclusive) -->
952 <!ATTLIST "JFIFthumbPalette" "thumbHeight" #CDATA #IMPLIED>
953 <!-- The height of the thumbnail -->
954 <!-- Data type: Integer -->
955 <!-- Min value: 0 (inclusive) -->
956 <!-- Max value: 255 (inclusive) -->
957
958 <!ELEMENT "JFIFthumbRGB" EMPTY>
959 <!-- A JFIF thumbnail as an RGB image -->
960 <!ATTLIST "JFIFthumbRGB" "thumbWidth" #CDATA #IMPLIED>
961 <!-- The width of the thumbnail -->
962 <!-- Data type: Integer -->
963 <!-- Min value: 0 (inclusive) -->
964 <!-- Max value: 255 (inclusive) -->
965 <!ATTLIST "JFIFthumbRGB" "thumbHeight" #CDATA #IMPLIED>
966 <!-- The height of the thumbnail -->
967 <!-- Data type: Integer -->
968 <!-- Min value: 0 (inclusive) -->
969 <!-- Max value: 255 (inclusive) -->
970
971 <!ELEMENT "app2ICC" EMPTY>
972 <!-- An ICC profile APP2 marker segment -->
973 <!-- Optional User object: java.awt.color.ICC_Profile -->
974
975 <!ELEMENT "markerSequence" (dqt | dht | dri | com | unknown |
976 app14Adobe | sof | sos)*>
977 <!-- A node grouping all non-jfif marker segments -->
978
979 <!ELEMENT "dqt" (dqtable)*>
980 <!-- A Define Quantization Table(s) marker segment -->
981 <!-- Min children: 1 -->
982 <!-- Max children: 4 -->
983
984 <!ELEMENT "dqtable" EMPTY>
985 <!-- A single quantization table -->
986 <!-- User object: javax.imageio.plugins.jpeg.JPEGQTable -->
987 <!ATTLIST "dqtable" "elementPrecision" #CDATA "0">
988 <!-- The number of bits in each table element (0 = 8, 1 = 16)
989 -->
990 <!-- Data type: Integer -->
991 <!ATTLIST "dqtable" "qtableId" ("0" | "1" | "2" | "3") #REQUIRED>
992
993 <!ELEMENT "dht" (dhtable)*>
994 <!-- A Define Huffman Table(s) marker segment -->
995 <!-- Min children: 1 -->
996 <!-- Max children: 4 -->
997
998 <!ELEMENT "dhtable" EMPTY>
999 <!-- A single Huffman table -->
1000 <!-- User object: javax.imageio.plugins.jpeg.JPEGHuffmanTable -->
1001 <!ATTLIST "dhtable" "class" ("0" | "1") #REQUIRED>
1002 <!-- Indicates whether this is a DC (0) or an AC (1) table -->
1003 <!ATTLIST "dhtable" "htableId" ("0" | "1" | "2" | "3") #REQUIRED>
1004 <!-- The table id -->
1005
1006 <!ELEMENT "dri" EMPTY>
1007 <!-- A Define Restart Interval marker segment -->
1008 <!ATTLIST "dri" "interval" #CDATA #REQUIRED>
1009 <!-- The restart interval in MCUs -->
1010 <!-- Data type: Integer -->
1011 <!-- Min value: 0 (inclusive) -->
1012 <!-- Max value: 65535 (inclusive) -->
1013
1014 <!ELEMENT "com" EMPTY>
1015 <!-- A Comment marker segment. The user object contains the actual
1016 bytes. -->
1017 <!-- User object: array of [B -->
1018 <!-- Min length: 1 -->
1019 <!-- Max length: 65533 -->
1020 <!ATTLIST "com" "comment" #CDATA #IMPLIED>
1021 <!-- The comment as a string (used only if user object is null)
1022 -->
1023 <!-- Data type: String -->
1024
1025 <!ELEMENT "unknown" EMPTY>
1026 <!-- An unrecognized marker segment. The user object contains the
1027 data not including length. -->
1028 <!-- User object: array of [B -->
1029 <!-- Min length: 1 -->
1030 <!-- Max length: 65533 -->
1031 <!ATTLIST "unknown" "MarkerTag" #CDATA #REQUIRED>
1032 <!-- The tag identifying this marker segment -->
1033 <!-- Data type: Integer -->
1034 <!-- Min value: 0 (inclusive) -->
1035 <!-- Max value: 255 (inclusive) -->
1036
1037 <!ELEMENT "app14Adobe" EMPTY>
1038 <!-- An Adobe APP14 marker segment -->
1039 <!ATTLIST "app14Adobe" "version" #CDATA "100">
1040 <!-- The version of Adobe APP14 marker segment -->
1041 <!-- Data type: Integer -->
1042 <!-- Min value: 100 (inclusive) -->
1043 <!-- Max value: 255 (inclusive) -->
1044 <!ATTLIST "app14Adobe" "flags0" #CDATA "0">
1045 <!-- The flags0 variable of an APP14 marker segment -->
1046 <!-- Data type: Integer -->
1047 <!-- Min value: 0 (inclusive) -->
1048 <!-- Max value: 65535 (inclusive) -->
1049 <!ATTLIST "app14Adobe" "flags1" #CDATA "0">
1050 <!-- The flags1 variable of an APP14 marker segment -->
1051 <!-- Data type: Integer -->
1052 <!-- Min value: 0 (inclusive) -->
1053 <!-- Max value: 65535 (inclusive) -->
1054 <!ATTLIST "app14Adobe" "transform" ("0" | "1" | "2") #REQUIRED>
1055 <!-- The color transform applied to the image (0 = Unknown, 1 =
1056 YCbCr, 2 = YCCK) -->
1057
1058 <!ELEMENT "sof" (componentSpec)*>
1059 <!-- A Start Of Frame marker segment -->
1060 <!-- Min children: 1 -->
1061 <!-- Max children: 4 -->
1062 <!ATTLIST "sof" "process" ("0" | "1" | "2") #IMPLIED>
1063 <!-- The JPEG process (0 = Baseline sequential, 1 = Extended
1064 sequential, 2 = Progressive) -->
1065 <!ATTLIST "sof" "samplePrecision" #CDATA "8">
1066 <!-- The number of bits per sample -->
1067 <!-- Data type: Integer -->
1068 <!ATTLIST "sof" "numLines" #CDATA #IMPLIED>
1069 <!-- The number of lines in the image -->
1070 <!-- Data type: Integer -->
1071 <!-- Min value: 0 (inclusive) -->
1072 <!-- Max value: 65535 (inclusive) -->
1073 <!ATTLIST "sof" "samplesPerLine" #CDATA #IMPLIED>
1074 <!-- The number of samples per line -->
1075 <!-- Data type: Integer -->
1076 <!-- Min value: 0 (inclusive) -->
1077 <!-- Max value: 65535 (inclusive) -->
1078 <!ATTLIST "sof" "numFrameComponents" ("1" | "2" | "3" | "4")
1079 #IMPLIED>
1080 <!-- The number of components in the image -->
1081
1082 <!ELEMENT "componentSpec" EMPTY>
1083 <!-- A component specification for a frame -->
1084 <!ATTLIST "componentSpec" "componentId" #CDATA #REQUIRED>
1085 <!-- The id for this component -->
1086 <!-- Data type: Integer -->
1087 <!-- Min value: 0 (inclusive) -->
1088 <!-- Max value: 255 (inclusive) -->
1089 <!ATTLIST "componentSpec" "HsamplingFactor" #CDATA #REQUIRED>
1090 <!-- The horizontal sampling factor for this component -->
1091 <!-- Data type: Integer -->
1092 <!-- Min value: 1 (inclusive) -->
1093 <!-- Max value: 255 (inclusive) -->
1094 <!ATTLIST "componentSpec" "VsamplingFactor" #CDATA #REQUIRED>
1095 <!-- The vertical sampling factor for this component -->
1096 <!-- Data type: Integer -->
1097 <!-- Min value: 1 (inclusive) -->
1098 <!-- Max value: 255 (inclusive) -->
1099 <!ATTLIST "componentSpec" "QtableSelector" ("0" | "1" | "2" |
1100 "3") #REQUIRED>
1101 <!-- The quantization table to use for this component -->
1102
1103 <!ELEMENT "sos" (scanComponentSpec)*>
1104 <!-- A Start Of Scan marker segment -->
1105 <!-- Min children: 1 -->
1106 <!-- Max children: 4 -->
1107 <!ATTLIST "sos" "numScanComponents" ("1" | "2" | "3" | "4")
1108 #REQUIRED>
1109 <!-- The number of components in the scan -->
1110 <!ATTLIST "sos" "startSpectralSelection" #CDATA "0">
1111 <!-- The first spectral band included in this scan -->
1112 <!-- Data type: Integer -->
1113 <!-- Min value: 0 (inclusive) -->
1114 <!-- Max value: 63 (inclusive) -->
1115 <!ATTLIST "sos" "endSpectralSelection" #CDATA "63">
1116 <!-- The last spectral band included in this scan -->
1117 <!-- Data type: Integer -->
1118 <!-- Min value: 0 (inclusive) -->
1119 <!-- Max value: 63 (inclusive) -->
1120 <!ATTLIST "sos" "approxHigh" #CDATA "0">
1121 <!-- The highest bit position included in this scan -->
1122 <!-- Data type: Integer -->
1123 <!-- Min value: 0 (inclusive) -->
1124 <!-- Max value: 15 (inclusive) -->
1125 <!ATTLIST "sos" "approxLow" #CDATA "0">
1126 <!-- The lowest bit position included in this scan -->
1127 <!-- Data type: Integer -->
1128 <!-- Min value: 0 (inclusive) -->
1129 <!-- Max value: 15 (inclusive) -->
1130
1131 <!ELEMENT "scanComponentSpec" EMPTY>
1132 <!-- A component specification for a scan -->
1133 <!ATTLIST "scanComponentSpec" "componentSelector" #CDATA
1134 #REQUIRED>
1135 <!-- The id of this component -->
1136 <!-- Data type: Integer -->
1137 <!-- Min value: 0 (inclusive) -->
1138 <!-- Max value: 255 (inclusive) -->
1139 <!ATTLIST "scanComponentSpec" "dcHuffTable" ("0" | "1" | "2" |
1140 "3") #REQUIRED>
1141 <!-- The huffman table to use for encoding DC coefficients -->
1142 <!ATTLIST "scanComponentSpec" "acHuffTable" ("0" | "1" | "2" |
1143 "3") #REQUIRED>
1144 <!-- The huffman table to use for encoding AC coefficients -->
1145 ]>
1146 </pre>
1147
1148 <h2>
1149 <a id=stream>Stream Metadata DTD</a>
1150 </h2>
1151
1152 <pre>
1153 <!DOCTYPE "javax_imageio_jpeg_stream_1.0" [
1154 <!ELEMENT "javax_imageio_jpeg_stream_1.0" (dqt |
1155 dht |
1156 dri |
1157 com |
1158 unknown)*>
1159
1160 <!-- All elements are as defined above for image metadata -->
1161 ]>
1162 </pre>
1163 </div>
1164 </main>
1165 </body>
1166 </html>