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1 libjpeg-turbo note: This is the legacy document from the original libjpeg v6b 1 libjpeg-turbo note: This file is mostly taken from the libjpeg v8b README
2 release, which is included for reference. The Internet addresses given below 2 file, and it is included only for reference. Some parts of it may not apply to
3 are likely non-functional. For more information about the libjpeg project, 3 libjpeg-turbo. Please see README-turbo.txt for information specific to the
4 please see http://www.ijg.org. For more information about libjpeg-turbo, 4 turbo version.
5 please see http://libjpeg-turbo.virtualgl.org.
6 5
7 6
8 The Independent JPEG Group's JPEG software 7 The Independent JPEG Group's JPEG software
9 ========================================== 8 ==========================================
10 9
11 README for release 6b of 27-Mar-1998 10 This distribution contains a release of the Independent JPEG Group's free JPEG
12 ==================================== 11 software. You are welcome to redistribute this software and to use it for any
12 purpose, subject to the conditions under LEGAL ISSUES, below.
13 13
14 This distribution contains the sixth public release of the Independent JPEG 14 This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone,
15 Group's free JPEG software. You are welcome to redistribute this software and 15 Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson,
16 to use it for any purpose, subject to the conditions under LEGAL ISSUES, below. 16 Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers,
17 17 and other members of the Independent JPEG Group.
18 Serious users of this software (particularly those incorporating it into
19 larger programs) should contact IJG at jpeg-info@uunet.uu.net to be added to
20 our electronic mailing list. Mailing list members are notified of updates
21 and have a chance to participate in technical discussions, etc.
22
23 This software is the work of Tom Lane, Philip Gladstone, Jim Boucher,
24 Lee Crocker, Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi,
25 Guido Vollbeding, Ge' Weijers, and other members of the Independent JPEG
26 Group.
27 18
28 IJG is not affiliated with the official ISO JPEG standards committee. 19 IJG is not affiliated with the official ISO JPEG standards committee.
29 20
30 21
31 DOCUMENTATION ROADMAP 22 DOCUMENTATION ROADMAP
32 ===================== 23 =====================
33 24
34 This file contains the following sections: 25 This file contains the following sections:
35 26
36 OVERVIEW General description of JPEG and the IJG software. 27 OVERVIEW General description of JPEG and the IJG software.
37 LEGAL ISSUES Copyright, lack of warranty, terms of distribution. 28 LEGAL ISSUES Copyright, lack of warranty, terms of distribution.
38 REFERENCES Where to learn more about JPEG. 29 REFERENCES Where to learn more about JPEG.
39 ARCHIVE LOCATIONS Where to find newer versions of this software. 30 ARCHIVE LOCATIONS Where to find newer versions of this software.
40 RELATED SOFTWARE Other stuff you should get.
41 FILE FORMAT WARS Software *not* to get. 31 FILE FORMAT WARS Software *not* to get.
42 TO DO Plans for future IJG releases. 32 TO DO Plans for future IJG releases.
43 33
44 Other documentation files in the distribution are: 34 Other documentation files in the distribution are:
45 35
46 User documentation: 36 User documentation:
47 install.doc How to configure and install the IJG software. 37 install.txt How to configure and install the IJG software.
48 usage.doc Usage instructions for cjpeg, djpeg, jpegtran, 38 usage.txt Usage instructions for cjpeg, djpeg, jpegtran,
49 rdjpgcom, and wrjpgcom. 39 rdjpgcom, and wrjpgcom.
50 *.1 Unix-style man pages for programs (same info as usage.doc). 40 *.1 Unix-style man pages for programs (same info as usage.txt).
51 wizard.doc Advanced usage instructions for JPEG wizards only. 41 wizard.txt Advanced usage instructions for JPEG wizards only.
52 change.log Version-to-version change highlights. 42 change.log Version-to-version change highlights.
53 Programmer and internal documentation: 43 Programmer and internal documentation:
54 libjpeg.doc How to use the JPEG library in your own programs. 44 libjpeg.txt How to use the JPEG library in your own programs.
55 example.c Sample code for calling the JPEG library. 45 example.c Sample code for calling the JPEG library.
56 structure.doc Overview of the JPEG library's internal structure. 46 structure.txt Overview of the JPEG library's internal structure.
57 filelist.doc Road map of IJG files. 47 filelist.txt Road map of IJG files.
58 coderules.doc Coding style rules --- please read if you contribute code. 48 coderules.txt Coding style rules --- please read if you contribute code.
59 49
60 Please read at least the files install.doc and usage.doc. Useful information 50 Please read at least the files install.txt and usage.txt. Some information
61 can also be found in the JPEG FAQ (Frequently Asked Questions) article. See 51 can also be found in the JPEG FAQ (Frequently Asked Questions) article. See
62 ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. 52 ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.
63 53
64 If you want to understand how the JPEG code works, we suggest reading one or 54 If you want to understand how the JPEG code works, we suggest reading one or
65 more of the REFERENCES, then looking at the documentation files (in roughly 55 more of the REFERENCES, then looking at the documentation files (in roughly
66 the order listed) before diving into the code. 56 the order listed) before diving into the code.
67 57
68 58
69 OVERVIEW 59 OVERVIEW
70 ======== 60 ========
71 61
72 This package contains C software to implement JPEG image compression and 62 This package contains C software to implement JPEG image encoding, decoding,
73 decompression. JPEG (pronounced "jay-peg") is a standardized compression 63 and transcoding. JPEG (pronounced "jay-peg") is a standardized compression
74 method for full-color and gray-scale images. JPEG is intended for compressing 64 method for full-color and gray-scale images. JPEG's strong suit is compressing
75 "real-world" scenes; line drawings, cartoons and other non-realistic images 65 photographic images or other types of images which have smooth color and
76 are not its strong suit. JPEG is lossy, meaning that the output image is not 66 brightness transitions between neighboring pixels. Images with sharp lines or
77 exactly identical to the input image. Hence you must not use JPEG if you 67 other abrupt features may not compress well with JPEG, and a higher JPEG
78 have to have identical output bits. However, on typical photographic images, 68 quality may have to be used to avoid visible compression artifacts with such
79 very good compression levels can be obtained with no visible change, and 69 images.
80 remarkably high compression levels are possible if you can tolerate a 70
81 low-quality image. For more details, see the references, or just experiment 71 JPEG is lossy, meaning that the output pixels are not necessarily identical to
82 with various compression settings. 72 the input pixels. However, on photographic content and other "smooth" images,
73 very good compression ratios can be obtained with no visible compression
74 artifacts, and extremely high compression ratios are possible if you are
75 willing to sacrifice image quality (by reducing the "quality" setting in the
76 compressor.)
83 77
84 This software implements JPEG baseline, extended-sequential, and progressive 78 This software implements JPEG baseline, extended-sequential, and progressive
85 compression processes. Provision is made for supporting all variants of these 79 compression processes. Provision is made for supporting all variants of these
86 processes, although some uncommon parameter settings aren't implemented yet. 80 processes, although some uncommon parameter settings aren't implemented yet.
87 For legal reasons, we are not distributing code for the arithmetic-coding 81 We have made no provision for supporting the hierarchical or lossless
88 variants of JPEG; see LEGAL ISSUES. We have made no provision for supporting 82 processes defined in the standard.
89 the hierarchical or lossless processes defined in the standard.
90 83
91 We provide a set of library routines for reading and writing JPEG image files, 84 We provide a set of library routines for reading and writing JPEG image files,
92 plus two sample applications "cjpeg" and "djpeg", which use the library to 85 plus two sample applications "cjpeg" and "djpeg", which use the library to
93 perform conversion between JPEG and some other popular image file formats. 86 perform conversion between JPEG and some other popular image file formats.
94 The library is intended to be reused in other applications. 87 The library is intended to be reused in other applications.
95 88
96 In order to support file conversion and viewing software, we have included 89 In order to support file conversion and viewing software, we have included
97 considerable functionality beyond the bare JPEG coding/decoding capability; 90 considerable functionality beyond the bare JPEG coding/decoding capability;
98 for example, the color quantization modules are not strictly part of JPEG 91 for example, the color quantization modules are not strictly part of JPEG
99 decoding, but they are essential for output to colormapped file formats or 92 decoding, but they are essential for output to colormapped file formats or
100 colormapped displays. These extra functions can be compiled out of the 93 colormapped displays. These extra functions can be compiled out of the
101 library if not required for a particular application. We have also included 94 library if not required for a particular application.
102 "jpegtran", a utility for lossless transcoding between different JPEG 95
103 processes, and "rdjpgcom" and "wrjpgcom", two simple applications for 96 We have also included "jpegtran", a utility for lossless transcoding between
104 inserting and extracting textual comments in JFIF files. 97 different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple
98 applications for inserting and extracting textual comments in JFIF files.
105 99
106 The emphasis in designing this software has been on achieving portability and 100 The emphasis in designing this software has been on achieving portability and
107 flexibility, while also making it fast enough to be useful. In particular, 101 flexibility, while also making it fast enough to be useful. In particular,
108 the software is not intended to be read as a tutorial on JPEG. (See the 102 the software is not intended to be read as a tutorial on JPEG. (See the
109 REFERENCES section for introductory material.) Rather, it is intended to 103 REFERENCES section for introductory material.) Rather, it is intended to
110 be reliable, portable, industrial-strength code. We do not claim to have 104 be reliable, portable, industrial-strength code. We do not claim to have
111 achieved that goal in every aspect of the software, but we strive for it. 105 achieved that goal in every aspect of the software, but we strive for it.
112 106
113 We welcome the use of this software as a component of commercial products. 107 We welcome the use of this software as a component of commercial products.
114 No royalty is required, but we do ask for an acknowledgement in product 108 No royalty is required, but we do ask for an acknowledgement in product
(...skipping 12 matching lines...) Expand all
127 program, you must acknowledge somewhere in your documentation that 121 program, you must acknowledge somewhere in your documentation that
128 you've used the IJG code. 122 you've used the IJG code.
129 123
130 In legalese: 124 In legalese:
131 125
132 The authors make NO WARRANTY or representation, either express or implied, 126 The authors make NO WARRANTY or representation, either express or implied,
133 with respect to this software, its quality, accuracy, merchantability, or 127 with respect to this software, its quality, accuracy, merchantability, or
134 fitness for a particular purpose. This software is provided "AS IS", and you, 128 fitness for a particular purpose. This software is provided "AS IS", and you,
135 its user, assume the entire risk as to its quality and accuracy. 129 its user, assume the entire risk as to its quality and accuracy.
136 130
137 This software is copyright (C) 1991-1998, Thomas G. Lane. 131 This software is copyright (C) 1991-2010, Thomas G. Lane, Guido Vollbeding.
138 All Rights Reserved except as specified below. 132 All Rights Reserved except as specified below.
139 133
140 Permission is hereby granted to use, copy, modify, and distribute this 134 Permission is hereby granted to use, copy, modify, and distribute this
141 software (or portions thereof) for any purpose, without fee, subject to these 135 software (or portions thereof) for any purpose, without fee, subject to these
142 conditions: 136 conditions:
143 (1) If any part of the source code for this software is distributed, then this 137 (1) If any part of the source code for this software is distributed, then this
144 README file must be included, with this copyright and no-warranty notice 138 README file must be included, with this copyright and no-warranty notice
145 unaltered; and any additions, deletions, or changes to the original files 139 unaltered; and any additions, deletions, or changes to the original files
146 must be clearly indicated in accompanying documentation. 140 must be clearly indicated in accompanying documentation.
147 (2) If only executable code is distributed, then the accompanying 141 (2) If only executable code is distributed, then the accompanying
(...skipping 22 matching lines...) Expand all
170 ansi2knr.c is NOT covered by the above copyright and conditions, but instead 164 ansi2knr.c is NOT covered by the above copyright and conditions, but instead
171 by the usual distribution terms of the Free Software Foundation; principally, 165 by the usual distribution terms of the Free Software Foundation; principally,
172 that you must include source code if you redistribute it. (See the file 166 that you must include source code if you redistribute it. (See the file
173 ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part 167 ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part
174 of any program generated from the IJG code, this does not limit you more than 168 of any program generated from the IJG code, this does not limit you more than
175 the foregoing paragraphs do. 169 the foregoing paragraphs do.
176 170
177 The Unix configuration script "configure" was produced with GNU Autoconf. 171 The Unix configuration script "configure" was produced with GNU Autoconf.
178 It is copyright by the Free Software Foundation but is freely distributable. 172 It is copyright by the Free Software Foundation but is freely distributable.
179 The same holds for its supporting scripts (config.guess, config.sub, 173 The same holds for its supporting scripts (config.guess, config.sub,
180 ltconfig, ltmain.sh). Another support script, install-sh, is copyright 174 ltmain.sh). Another support script, install-sh, is copyright by X Consortium
181 by M.I.T. but is also freely distributable. 175 but is also freely distributable.
182
183 It appears that the arithmetic coding option of the JPEG spec is covered by
184 patents owned by IBM, AT&T, and Mitsubishi. Hence arithmetic coding cannot
185 legally be used without obtaining one or more licenses. For this reason,
186 support for arithmetic coding has been removed from the free JPEG software.
187 (Since arithmetic coding provides only a marginal gain over the unpatented
188 Huffman mode, it is unlikely that very many implementations will support it.)
189 So far as we are aware, there are no patent restrictions on the remaining
190 code.
191 176
192 The IJG distribution formerly included code to read and write GIF files. 177 The IJG distribution formerly included code to read and write GIF files.
193 To avoid entanglement with the Unisys LZW patent, GIF reading support has 178 To avoid entanglement with the Unisys LZW patent, GIF reading support has
194 been removed altogether, and the GIF writer has been simplified to produce 179 been removed altogether, and the GIF writer has been simplified to produce
195 "uncompressed GIFs". This technique does not use the LZW algorithm; the 180 "uncompressed GIFs". This technique does not use the LZW algorithm; the
196 resulting GIF files are larger than usual, but are readable by all standard 181 resulting GIF files are larger than usual, but are readable by all standard
197 GIF decoders. 182 GIF decoders.
198 183
199 We are required to state that 184 We are required to state that
200 "The Graphics Interchange Format(c) is the Copyright property of 185 "The Graphics Interchange Format(c) is the Copyright property of
201 CompuServe Incorporated. GIF(sm) is a Service Mark property of 186 CompuServe Incorporated. GIF(sm) is a Service Mark property of
202 CompuServe Incorporated." 187 CompuServe Incorporated."
203 188
204 189
205 REFERENCES 190 REFERENCES
206 ========== 191 ==========
207 192
208 We highly recommend reading one or more of these references before trying to 193 We recommend reading one or more of these references before trying to
209 understand the innards of the JPEG software. 194 understand the innards of the JPEG software.
210 195
211 The best short technical introduction to the JPEG compression algorithm is 196 The best short technical introduction to the JPEG compression algorithm is
212 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", 197 Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
213 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. 198 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
214 (Adjacent articles in that issue discuss MPEG motion picture compression, 199 (Adjacent articles in that issue discuss MPEG motion picture compression,
215 applications of JPEG, and related topics.) If you don't have the CACM issue 200 applications of JPEG, and related topics.) If you don't have the CACM issue
216 handy, a PostScript file containing a revised version of Wallace's article is 201 handy, a PostScript file containing a revised version of Wallace's article is
217 available at ftp://ftp.uu.net/graphics/jpeg/wallace.ps.gz. The file (actually 202 available at http://www.ijg.org/files/wallace.ps.gz. The file (actually
218 a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 203 a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
219 omits the sample images that appeared in CACM, but it includes corrections 204 omits the sample images that appeared in CACM, but it includes corrections
220 and some added material. Note: the Wallace article is copyright ACM and IEEE, 205 and some added material. Note: the Wallace article is copyright ACM and IEEE,
221 and it may not be used for commercial purposes. 206 and it may not be used for commercial purposes.
222 207
223 A somewhat less technical, more leisurely introduction to JPEG can be found in 208 A somewhat less technical, more leisurely introduction to JPEG can be found in
224 "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by 209 "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by
225 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 210 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides
226 good explanations and example C code for a multitude of compression methods 211 good explanations and example C code for a multitude of compression methods
227 including JPEG. It is an excellent source if you are comfortable reading C 212 including JPEG. It is an excellent source if you are comfortable reading C
228 code but don't know much about data compression in general. The book's JPEG 213 code but don't know much about data compression in general. The book's JPEG
229 sample code is far from industrial-strength, but when you are ready to look 214 sample code is far from industrial-strength, but when you are ready to look
230 at a full implementation, you've got one here... 215 at a full implementation, you've got one here...
231 216
232 The best full description of JPEG is the textbook "JPEG Still Image Data 217 The best currently available description of JPEG is the textbook "JPEG Still
233 Compression Standard" by William B. Pennebaker and Joan L. Mitchell, published 218 Image Data Compression Standard" by William B. Pennebaker and Joan L.
234 by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. Price US$59.95, 638 pp. 219 Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
235 The book includes the complete text of the ISO JPEG standards (DIS 10918-1 220 Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG
236 and draft DIS 10918-2). This is by far the most complete exposition of JPEG 221 standards (DIS 10918-1 and draft DIS 10918-2).
237 in existence, and we highly recommend it.
238 222
239 The JPEG standard itself is not available electronically; you must order a 223 The original JPEG standard is divided into two parts, Part 1 being the actual
240 paper copy through ISO or ITU. (Unless you feel a need to own a certified 224 specification, while Part 2 covers compliance testing methods. Part 1 is
241 official copy, we recommend buying the Pennebaker and Mitchell book instead; 225 titled "Digital Compression and Coding of Continuous-tone Still Images,
242 it's much cheaper and includes a great deal of useful explanatory material.)
243 In the USA, copies of the standard may be ordered from ANSI Sales at (212)
244 642-4900, or from Global Engineering Documents at (800) 854-7179. (ANSI
245 doesn't take credit card orders, but Global does.) It's not cheap: as of
246 1992, ANSI was charging $95 for Part 1 and $47 for Part 2, plus 7%
247 shipping/handling. The standard is divided into two parts, Part 1 being the
248 actual specification, while Part 2 covers compliance testing methods. Part 1
249 is titled "Digital Compression and Coding of Continuous-tone Still Images,
250 Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 226 Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
251 10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 227 10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of
252 Continuous-tone Still Images, Part 2: Compliance testing" and has document 228 Continuous-tone Still Images, Part 2: Compliance testing" and has document
253 numbers ISO/IEC IS 10918-2, ITU-T T.83. 229 numbers ISO/IEC IS 10918-2, ITU-T T.83.
254 230
255 Some extensions to the original JPEG standard are defined in JPEG Part 3,
256 a newer ISO standard numbered ISO/IEC IS 10918-3 and ITU-T T.84. IJG
257 currently does not support any Part 3 extensions.
258
259 The JPEG standard does not specify all details of an interchangeable file 231 The JPEG standard does not specify all details of an interchangeable file
260 format. For the omitted details we follow the "JFIF" conventions, revision 232 format. For the omitted details we follow the "JFIF" conventions, revision
261 1.02. A copy of the JFIF spec is available from: 233 1.02. JFIF 1.02 has been adopted as an Ecma International Technical Report
262 » Literature Department 234 and thus received a formal publication status. It is available as a free
263 » C-Cube Microsystems, Inc. 235 download in PDF format from
264 » 1778 McCarthy Blvd. 236 http://www.ecma-international.org/publications/techreports/E-TR-098.htm.
265 » Milpitas, CA 95035 237 A PostScript version of the JFIF document is available at
266 » phone (408) 944-6300, fax (408) 944-6314 238 http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at
267 A PostScript version of this document is available by FTP at 239 http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures.
268 ftp://ftp.uu.net/graphics/jpeg/jfif.ps.gz. There is also a plain text
269 version at ftp://ftp.uu.net/graphics/jpeg/jfif.txt.gz, but it is missing
270 the figures.
271 240
272 The TIFF 6.0 file format specification can be obtained by FTP from 241 The TIFF 6.0 file format specification can be obtained by FTP from
273 ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 242 ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme
274 found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 243 found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.
275 IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 244 IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).
276 Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 245 Instead, we recommend the JPEG design proposed by TIFF Technical Note #2
277 (Compression tag 7). Copies of this Note can be obtained from ftp.sgi.com or 246 (Compression tag 7). Copies of this Note can be obtained from
278 from ftp://ftp.uu.net/graphics/jpeg/. It is expected that the next revision 247 http://www.ijg.org/files/. It is expected that the next revision
279 of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 248 of the TIFF spec will replace the 6.0 JPEG design with the Note's design.
280 Although IJG's own code does not support TIFF/JPEG, the free libtiff library 249 Although IJG's own code does not support TIFF/JPEG, the free libtiff library
281 uses our library to implement TIFF/JPEG per the Note. libtiff is available 250 uses our library to implement TIFF/JPEG per the Note.
282 from ftp://ftp.sgi.com/graphics/tiff/.
283 251
284 252
285 ARCHIVE LOCATIONS 253 ARCHIVE LOCATIONS
286 ================= 254 =================
287 255
288 The "official" archive site for this software is ftp.uu.net (Internet 256 The "official" archive site for this software is www.ijg.org.
289 address 192.48.96.9). The most recent released version can always be found 257 The most recent released version can always be found there in
290 there in directory graphics/jpeg. This particular version will be archived 258 directory "files". This particular version will be archived as
291 as ftp://ftp.uu.net/graphics/jpeg/jpegsrc.v6b.tar.gz. If you don't have 259 http://www.ijg.org/files/jpegsrc.v8b.tar.gz, and in Windows-compatible
292 direct Internet access, UUNET's archives are also available via UUCP; contact 260 "zip" archive format as http://www.ijg.org/files/jpegsr8b.zip.
293 help@uunet.uu.net for information on retrieving files that way.
294 261
295 Numerous Internet sites maintain copies of the UUNET files. However, only 262 The JPEG FAQ (Frequently Asked Questions) article is a source of some
296 ftp.uu.net is guaranteed to have the latest official version. 263 general information about JPEG.
297
298 You can also obtain this software in DOS-compatible "zip" archive format from
299 the SimTel archives (ftp://ftp.simtel.net/pub/simtelnet/msdos/graphics/), or
300 on CompuServe in the Graphics Support forum (GO CIS:GRAPHSUP), library 12
301 "JPEG Tools". Again, these versions may sometimes lag behind the ftp.uu.net
302 release.
303
304 The JPEG FAQ (Frequently Asked Questions) article is a useful source of
305 general information about JPEG. It is updated constantly and therefore is
306 not included in this distribution. The FAQ is posted every two weeks to
307 Usenet newsgroups comp.graphics.misc, news.answers, and other groups.
308 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 264 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/
309 and other news.answers archive sites, including the official news.answers 265 and other news.answers archive sites, including the official news.answers
310 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 266 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.
311 If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu 267 If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu
312 with body 268 with body
313 send usenet/news.answers/jpeg-faq/part1 269 send usenet/news.answers/jpeg-faq/part1
314 send usenet/news.answers/jpeg-faq/part2 270 send usenet/news.answers/jpeg-faq/part2
315 271
316 272
317 RELATED SOFTWARE
318 ================
319
320 Numerous viewing and image manipulation programs now support JPEG. (Quite a
321 few of them use this library to do so.) The JPEG FAQ described above lists
322 some of the more popular free and shareware viewers, and tells where to
323 obtain them on Internet.
324
325 If you are on a Unix machine, we highly recommend Jef Poskanzer's free
326 PBMPLUS software, which provides many useful operations on PPM-format image
327 files. In particular, it can convert PPM images to and from a wide range of
328 other formats, thus making cjpeg/djpeg considerably more useful. The latest
329 version is distributed by the NetPBM group, and is available from numerous
330 sites, notably ftp://wuarchive.wustl.edu/graphics/graphics/packages/NetPBM/.
331 Unfortunately PBMPLUS/NETPBM is not nearly as portable as the IJG software is;
332 you are likely to have difficulty making it work on any non-Unix machine.
333
334 A different free JPEG implementation, written by the PVRG group at Stanford,
335 is available from ftp://havefun.stanford.edu/pub/jpeg/. This program
336 is designed for research and experimentation rather than production use;
337 it is slower, harder to use, and less portable than the IJG code, but it
338 is easier to read and modify. Also, the PVRG code supports lossless JPEG,
339 which we do not. (On the other hand, it doesn't do progressive JPEG.)
340
341
342 FILE FORMAT WARS 273 FILE FORMAT WARS
343 ================ 274 ================
344 275
345 Some JPEG programs produce files that are not compatible with our library. 276 The ISO JPEG standards committee actually promotes different formats like
346 The root of the problem is that the ISO JPEG committee failed to specify a 277 "JPEG 2000" or "JPEG XR" which are incompatible with original DCT-based
347 concrete file format. Some vendors "filled in the blanks" on their own, 278 JPEG. IJG therefore does not support these formats (see REFERENCES). Indeed,
348 creating proprietary formats that no one else could read. (For example, none
349 of the early commercial JPEG implementations for the Macintosh were able to
350 exchange compressed files.)
351
352 The file format we have adopted is called JFIF (see REFERENCES). This format
353 has been agreed to by a number of major commercial JPEG vendors, and it has
354 become the de facto standard. JFIF is a minimal or "low end" representation.
355 We recommend the use of TIFF/JPEG (TIFF revision 6.0 as modified by TIFF
356 Technical Note #2) for "high end" applications that need to record a lot of
357 additional data about an image. TIFF/JPEG is fairly new and not yet widely
358 supported, unfortunately.
359
360 The upcoming JPEG Part 3 standard defines a file format called SPIFF.
361 SPIFF is interoperable with JFIF, in the sense that most JFIF decoders should
362 be able to read the most common variant of SPIFF. SPIFF has some technical
363 advantages over JFIF, but its major claim to fame is simply that it is an
364 official standard rather than an informal one. At this point it is unclear
365 whether SPIFF will supersede JFIF or whether JFIF will remain the de-facto
366 standard. IJG intends to support SPIFF once the standard is frozen, but we
367 have not decided whether it should become our default output format or not.
368 (In any case, our decoder will remain capable of reading JFIF indefinitely.)
369
370 Various proprietary file formats incorporating JPEG compression also exist.
371 We have little or no sympathy for the existence of these formats. Indeed,
372 one of the original reasons for developing this free software was to help 279 one of the original reasons for developing this free software was to help
373 force convergence on common, open format standards for JPEG files. Don't 280 force convergence on common, interoperable format standards for JPEG files.
374 use a proprietary file format! 281 Don't use an incompatible file format!
282 (In any case, our decoder will remain capable of reading existing JPEG
283 image files indefinitely.)
375 284
376 285
377 TO DO 286 TO DO
378 ===== 287 =====
379 288
380 The major thrust for v7 will probably be improvement of visual quality. 289 Please send bug reports, offers of help, etc. to jpeg-info@uc.ag.
381 The current method for scaling the quantization tables is known not to be
382 very good at low Q values. We also intend to investigate block boundary
383 smoothing, "poor man's variable quantization", and other means of improving
384 quality-vs-file-size performance without sacrificing compatibility.
385
386 In future versions, we are considering supporting some of the upcoming JPEG
387 Part 3 extensions --- principally, variable quantization and the SPIFF file
388 format.
389
390 As always, speeding things up is of great interest.
391
392 Please send bug reports, offers of help, etc. to jpeg-info@uunet.uu.net.
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