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view libs/libjpeg/README @ 14:06dc8b9b4f89
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| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Sun, 07 Jun 2015 17:25:49 +0300 |
| parents | |
| children |
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1 The Independent JPEG Group's JPEG software
2 ==========================================
4 README for release 8c of 16-Jan-2011
5 ====================================
7 This distribution contains the eighth public release of the Independent JPEG
8 Group's free JPEG software. You are welcome to redistribute this software and
9 to use it for any purpose, subject to the conditions under LEGAL ISSUES, below.
11 This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone,
12 Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson,
13 Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers,
14 and other members of the Independent JPEG Group.
16 IJG is not affiliated with the official ISO JPEG standards committee.
19 DOCUMENTATION ROADMAP
20 =====================
22 This file contains the following sections:
24 OVERVIEW General description of JPEG and the IJG software.
25 LEGAL ISSUES Copyright, lack of warranty, terms of distribution.
26 REFERENCES Where to learn more about JPEG.
27 ARCHIVE LOCATIONS Where to find newer versions of this software.
28 ACKNOWLEDGMENTS Special thanks.
29 FILE FORMAT WARS Software *not* to get.
30 TO DO Plans for future IJG releases.
32 Other documentation files in the distribution are:
34 User documentation:
35 install.txt How to configure and install the IJG software.
36 usage.txt Usage instructions for cjpeg, djpeg, jpegtran,
37 rdjpgcom, and wrjpgcom.
38 *.1 Unix-style man pages for programs (same info as usage.txt).
39 wizard.txt Advanced usage instructions for JPEG wizards only.
40 change.log Version-to-version change highlights.
41 Programmer and internal documentation:
42 libjpeg.txt How to use the JPEG library in your own programs.
43 example.c Sample code for calling the JPEG library.
44 structure.txt Overview of the JPEG library's internal structure.
45 filelist.txt Road map of IJG files.
46 coderules.txt Coding style rules --- please read if you contribute code.
48 Please read at least the files install.txt and usage.txt. Some information
49 can also be found in the JPEG FAQ (Frequently Asked Questions) article. See
50 ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.
52 If you want to understand how the JPEG code works, we suggest reading one or
53 more of the REFERENCES, then looking at the documentation files (in roughly
54 the order listed) before diving into the code.
57 OVERVIEW
58 ========
60 This package contains C software to implement JPEG image encoding, decoding,
61 and transcoding. JPEG (pronounced "jay-peg") is a standardized compression
62 method for full-color and gray-scale images.
64 This software implements JPEG baseline, extended-sequential, and progressive
65 compression processes. Provision is made for supporting all variants of these
66 processes, although some uncommon parameter settings aren't implemented yet.
67 We have made no provision for supporting the hierarchical or lossless
68 processes defined in the standard.
70 We provide a set of library routines for reading and writing JPEG image files,
71 plus two sample applications "cjpeg" and "djpeg", which use the library to
72 perform conversion between JPEG and some other popular image file formats.
73 The library is intended to be reused in other applications.
75 In order to support file conversion and viewing software, we have included
76 considerable functionality beyond the bare JPEG coding/decoding capability;
77 for example, the color quantization modules are not strictly part of JPEG
78 decoding, but they are essential for output to colormapped file formats or
79 colormapped displays. These extra functions can be compiled out of the
80 library if not required for a particular application.
82 We have also included "jpegtran", a utility for lossless transcoding between
83 different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple
84 applications for inserting and extracting textual comments in JFIF files.
86 The emphasis in designing this software has been on achieving portability and
87 flexibility, while also making it fast enough to be useful. In particular,
88 the software is not intended to be read as a tutorial on JPEG. (See the
89 REFERENCES section for introductory material.) Rather, it is intended to
90 be reliable, portable, industrial-strength code. We do not claim to have
91 achieved that goal in every aspect of the software, but we strive for it.
93 We welcome the use of this software as a component of commercial products.
94 No royalty is required, but we do ask for an acknowledgement in product
95 documentation, as described under LEGAL ISSUES.
98 LEGAL ISSUES
99 ============
101 In plain English:
103 1. We don't promise that this software works. (But if you find any bugs,
104 please let us know!)
105 2. You can use this software for whatever you want. You don't have to pay us.
106 3. You may not pretend that you wrote this software. If you use it in a
107 program, you must acknowledge somewhere in your documentation that
108 you've used the IJG code.
110 In legalese:
112 The authors make NO WARRANTY or representation, either express or implied,
113 with respect to this software, its quality, accuracy, merchantability, or
114 fitness for a particular purpose. This software is provided "AS IS", and you,
115 its user, assume the entire risk as to its quality and accuracy.
117 This software is copyright (C) 1991-2011, Thomas G. Lane, Guido Vollbeding.
118 All Rights Reserved except as specified below.
120 Permission is hereby granted to use, copy, modify, and distribute this
121 software (or portions thereof) for any purpose, without fee, subject to these
122 conditions:
123 (1) If any part of the source code for this software is distributed, then this
124 README file must be included, with this copyright and no-warranty notice
125 unaltered; and any additions, deletions, or changes to the original files
126 must be clearly indicated in accompanying documentation.
127 (2) If only executable code is distributed, then the accompanying
128 documentation must state that "this software is based in part on the work of
129 the Independent JPEG Group".
130 (3) Permission for use of this software is granted only if the user accepts
131 full responsibility for any undesirable consequences; the authors accept
132 NO LIABILITY for damages of any kind.
134 These conditions apply to any software derived from or based on the IJG code,
135 not just to the unmodified library. If you use our work, you ought to
136 acknowledge us.
138 Permission is NOT granted for the use of any IJG author's name or company name
139 in advertising or publicity relating to this software or products derived from
140 it. This software may be referred to only as "the Independent JPEG Group's
141 software".
143 We specifically permit and encourage the use of this software as the basis of
144 commercial products, provided that all warranty or liability claims are
145 assumed by the product vendor.
148 ansi2knr.c is included in this distribution by permission of L. Peter Deutsch,
149 sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA.
150 ansi2knr.c is NOT covered by the above copyright and conditions, but instead
151 by the usual distribution terms of the Free Software Foundation; principally,
152 that you must include source code if you redistribute it. (See the file
153 ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part
154 of any program generated from the IJG code, this does not limit you more than
155 the foregoing paragraphs do.
157 The Unix configuration script "configure" was produced with GNU Autoconf.
158 It is copyright by the Free Software Foundation but is freely distributable.
159 The same holds for its supporting scripts (config.guess, config.sub,
160 ltmain.sh). Another support script, install-sh, is copyright by X Consortium
161 but is also freely distributable.
163 The IJG distribution formerly included code to read and write GIF files.
164 To avoid entanglement with the Unisys LZW patent, GIF reading support has
165 been removed altogether, and the GIF writer has been simplified to produce
166 "uncompressed GIFs". This technique does not use the LZW algorithm; the
167 resulting GIF files are larger than usual, but are readable by all standard
168 GIF decoders.
170 We are required to state that
171 "The Graphics Interchange Format(c) is the Copyright property of
172 CompuServe Incorporated. GIF(sm) is a Service Mark property of
173 CompuServe Incorporated."
176 REFERENCES
177 ==========
179 We recommend reading one or more of these references before trying to
180 understand the innards of the JPEG software.
182 The best short technical introduction to the JPEG compression algorithm is
183 Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
184 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
185 (Adjacent articles in that issue discuss MPEG motion picture compression,
186 applications of JPEG, and related topics.) If you don't have the CACM issue
187 handy, a PostScript file containing a revised version of Wallace's article is
188 available at http://www.ijg.org/files/wallace.ps.gz. The file (actually
189 a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
190 omits the sample images that appeared in CACM, but it includes corrections
191 and some added material. Note: the Wallace article is copyright ACM and IEEE,
192 and it may not be used for commercial purposes.
194 A somewhat less technical, more leisurely introduction to JPEG can be found in
195 "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by
196 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides
197 good explanations and example C code for a multitude of compression methods
198 including JPEG. It is an excellent source if you are comfortable reading C
199 code but don't know much about data compression in general. The book's JPEG
200 sample code is far from industrial-strength, but when you are ready to look
201 at a full implementation, you've got one here...
203 The best currently available description of JPEG is the textbook "JPEG Still
204 Image Data Compression Standard" by William B. Pennebaker and Joan L.
205 Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
206 Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG
207 standards (DIS 10918-1 and draft DIS 10918-2).
208 Although this is by far the most detailed and comprehensive exposition of
209 JPEG publicly available, we point out that it is still missing an explanation
210 of the most essential properties and algorithms of the underlying DCT
211 technology.
212 If you think that you know about DCT-based JPEG after reading this book,
213 then you are in delusion. The real fundamentals and corresponding potential
214 of DCT-based JPEG are not publicly known so far, and that is the reason for
215 all the mistaken developments taking place in the image coding domain.
217 The original JPEG standard is divided into two parts, Part 1 being the actual
218 specification, while Part 2 covers compliance testing methods. Part 1 is
219 titled "Digital Compression and Coding of Continuous-tone Still Images,
220 Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
221 10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of
222 Continuous-tone Still Images, Part 2: Compliance testing" and has document
223 numbers ISO/IEC IS 10918-2, ITU-T T.83.
224 IJG JPEG 8 introduces an implementation of the JPEG SmartScale extension
225 which is specified in a contributed document at ITU and ISO with title "ITU-T
226 JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced Image Coding", April
227 2006, Geneva, Switzerland. The latest version of the document is Revision 3.
229 The JPEG standard does not specify all details of an interchangeable file
230 format. For the omitted details we follow the "JFIF" conventions, revision
231 1.02. JFIF 1.02 has been adopted as an Ecma International Technical Report
232 and thus received a formal publication status. It is available as a free
233 download in PDF format from
234 http://www.ecma-international.org/publications/techreports/E-TR-098.htm.
235 A PostScript version of the JFIF document is available at
236 http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at
237 http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures.
239 The TIFF 6.0 file format specification can be obtained by FTP from
240 ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme
241 found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.
242 IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).
243 Instead, we recommend the JPEG design proposed by TIFF Technical Note #2
244 (Compression tag 7). Copies of this Note can be obtained from
245 http://www.ijg.org/files/. It is expected that the next revision
246 of the TIFF spec will replace the 6.0 JPEG design with the Note's design.
247 Although IJG's own code does not support TIFF/JPEG, the free libtiff library
248 uses our library to implement TIFF/JPEG per the Note.
251 ARCHIVE LOCATIONS
252 =================
254 The "official" archive site for this software is www.ijg.org.
255 The most recent released version can always be found there in
256 directory "files". This particular version will be archived as
257 http://www.ijg.org/files/jpegsrc.v8c.tar.gz, and in Windows-compatible
258 "zip" archive format as http://www.ijg.org/files/jpegsr8c.zip.
260 The JPEG FAQ (Frequently Asked Questions) article is a source of some
261 general information about JPEG.
262 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/
263 and other news.answers archive sites, including the official news.answers
264 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.
265 If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu
266 with body
267 send usenet/news.answers/jpeg-faq/part1
268 send usenet/news.answers/jpeg-faq/part2
271 ACKNOWLEDGMENTS
272 ===============
274 Thank to Juergen Bruder for providing me with a copy of the common DCT
275 algorithm article, only to find out that I had come to the same result
276 in a more direct and comprehensible way with a more generative approach.
278 Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the
279 ITU JPEG (Study Group 16) meeting in Geneva, Switzerland.
281 Thank to Thomas Wiegand and Gary Sullivan for inviting me to the
282 Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland.
284 Thank to John Korejwa and Massimo Ballerini for inviting me to
285 fruitful consultations in Boston, MA and Milan, Italy.
287 Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther
288 Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel
289 for corresponding business development.
291 Thank to Nico Zschach and Dirk Stelling of the technical support team
292 at the Digital Images company in Halle for providing me with extra
293 equipment for configuration tests.
295 Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful
296 communication about JPEG configuration in Sigma Photo Pro software.
298 Thank to Andrew Finkenstadt for hosting the ijg.org site.
300 Last but not least special thank to Thomas G. Lane for the original
301 design and development of this singular software package.
304 FILE FORMAT WARS
305 ================
307 The ISO JPEG standards committee actually promotes different formats like
308 "JPEG 2000" or "JPEG XR" which are incompatible with original DCT-based
309 JPEG and which are based on faulty technologies. IJG therefore does not
310 and will not support such momentary mistakes (see REFERENCES).
311 We have little or no sympathy for the promotion of these formats. Indeed,
312 one of the original reasons for developing this free software was to help
313 force convergence on common, interoperable format standards for JPEG files.
314 Don't use an incompatible file format!
315 (In any case, our decoder will remain capable of reading existing JPEG
316 image files indefinitely.)
319 TO DO
320 =====
322 Version 8 is the first release of a new generation JPEG standard
323 to overcome the limitations of the original JPEG specification.
324 More features are being prepared for coming releases...
326 Please send bug reports, offers of help, etc. to jpeg-info@uc.ag.