source: trunk/libjpeg/README @ 283

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1The Independent JPEG Group's JPEG software
2==========================================
3
4README for release 7 of 27-Jun-2009
5===================================
6
7This distribution contains the seventh public release of the Independent JPEG
8Group's free JPEG software.  You are welcome to redistribute this software and
9to use it for any purpose, subject to the conditions under LEGAL ISSUES, below.
10
11This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone,
12Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson,
13Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers,
14and other members of the Independent JPEG Group.
15
16IJG is not affiliated with the official ISO JPEG standards committee.
17
18
19DOCUMENTATION ROADMAP
20=====================
21
22This file contains the following sections:
23
24OVERVIEW            General description of JPEG and the IJG software.
25LEGAL ISSUES        Copyright, lack of warranty, terms of distribution.
26REFERENCES          Where to learn more about JPEG.
27ARCHIVE LOCATIONS   Where to find newer versions of this software.
28ACKNOWLEDGMENTS     Special thanks.
29FILE FORMAT WARS    Software *not* to get.
30TO DO               Plans for future IJG releases.
31
32Other documentation files in the distribution are:
33
34User 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.
41Programmer 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.
47
48Please read at least the files install.txt and usage.txt.  Some information
49can also be found in the JPEG FAQ (Frequently Asked Questions) article.  See
50ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.
51
52If you want to understand how the JPEG code works, we suggest reading one or
53more of the REFERENCES, then looking at the documentation files (in roughly
54the order listed) before diving into the code.
55
56
57OVERVIEW
58========
59
60This package contains C software to implement JPEG image encoding, decoding,
61and transcoding.  JPEG (pronounced "jay-peg") is a standardized compression
62method for full-color and gray-scale images.
63
64This software implements JPEG baseline, extended-sequential, and progressive
65compression processes.  Provision is made for supporting all variants of these
66processes, although some uncommon parameter settings aren't implemented yet.
67We have made no provision for supporting the hierarchical or lossless
68processes defined in the standard.
69
70We provide a set of library routines for reading and writing JPEG image files,
71plus two sample applications "cjpeg" and "djpeg", which use the library to
72perform conversion between JPEG and some other popular image file formats.
73The library is intended to be reused in other applications.
74
75In order to support file conversion and viewing software, we have included
76considerable functionality beyond the bare JPEG coding/decoding capability;
77for example, the color quantization modules are not strictly part of JPEG
78decoding, but they are essential for output to colormapped file formats or
79colormapped displays.  These extra functions can be compiled out of the
80library if not required for a particular application.
81
82We have also included "jpegtran", a utility for lossless transcoding between
83different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple
84applications for inserting and extracting textual comments in JFIF files.
85
86The emphasis in designing this software has been on achieving portability and
87flexibility, while also making it fast enough to be useful.  In particular,
88the software is not intended to be read as a tutorial on JPEG.  (See the
89REFERENCES section for introductory material.)  Rather, it is intended to
90be reliable, portable, industrial-strength code.  We do not claim to have
91achieved that goal in every aspect of the software, but we strive for it.
92
93We welcome the use of this software as a component of commercial products.
94No royalty is required, but we do ask for an acknowledgement in product
95documentation, as described under LEGAL ISSUES.
96
97
98LEGAL ISSUES
99============
100
101In plain English:
102
1031. We don't promise that this software works.  (But if you find any bugs,
104   please let us know!)
1052. You can use this software for whatever you want.  You don't have to pay us.
1063. 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.
109
110In legalese:
111
112The authors make NO WARRANTY or representation, either express or implied,
113with respect to this software, its quality, accuracy, merchantability, or
114fitness for a particular purpose.  This software is provided "AS IS", and you,
115its user, assume the entire risk as to its quality and accuracy.
116
117This software is copyright (C) 1991-2009, Thomas G. Lane, Guido Vollbeding.
118All Rights Reserved except as specified below.
119
120Permission is hereby granted to use, copy, modify, and distribute this
121software (or portions thereof) for any purpose, without fee, subject to these
122conditions:
123(1) If any part of the source code for this software is distributed, then this
124README file must be included, with this copyright and no-warranty notice
125unaltered; and any additions, deletions, or changes to the original files
126must be clearly indicated in accompanying documentation.
127(2) If only executable code is distributed, then the accompanying
128documentation must state that "this software is based in part on the work of
129the Independent JPEG Group".
130(3) Permission for use of this software is granted only if the user accepts
131full responsibility for any undesirable consequences; the authors accept
132NO LIABILITY for damages of any kind.
133
134These conditions apply to any software derived from or based on the IJG code,
135not just to the unmodified library.  If you use our work, you ought to
136acknowledge us.
137
138Permission is NOT granted for the use of any IJG author's name or company name
139in advertising or publicity relating to this software or products derived from
140it.  This software may be referred to only as "the Independent JPEG Group's
141software".
142
143We specifically permit and encourage the use of this software as the basis of
144commercial products, provided that all warranty or liability claims are
145assumed by the product vendor.
146
147
148ansi2knr.c is included in this distribution by permission of L. Peter Deutsch,
149sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA.
150ansi2knr.c is NOT covered by the above copyright and conditions, but instead
151by the usual distribution terms of the Free Software Foundation; principally,
152that you must include source code if you redistribute it.  (See the file
153ansi2knr.c for full details.)  However, since ansi2knr.c is not needed as part
154of any program generated from the IJG code, this does not limit you more than
155the foregoing paragraphs do.
156
157The Unix configuration script "configure" was produced with GNU Autoconf.
158It is copyright by the Free Software Foundation but is freely distributable.
159The same holds for its supporting scripts (config.guess, config.sub,
160ltmain.sh).  Another support script, install-sh, is copyright by X Consortium
161but is also freely distributable.
162
163The IJG distribution formerly included code to read and write GIF files.
164To avoid entanglement with the Unisys LZW patent, GIF reading support has
165been removed altogether, and the GIF writer has been simplified to produce
166"uncompressed GIFs".  This technique does not use the LZW algorithm; the
167resulting GIF files are larger than usual, but are readable by all standard
168GIF decoders.
169
170We 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."
174
175
176REFERENCES
177==========
178
179We recommend reading one or more of these references before trying to
180understand the innards of the JPEG software.
181
182The 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,
186applications of JPEG, and related topics.)  If you don't have the CACM issue
187handy, a PostScript file containing a revised version of Wallace's article is
188available at http://www.ijg.org/files/wallace.ps.gz.  The file (actually
189a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
190omits the sample images that appeared in CACM, but it includes corrections
191and some added material.  Note: the Wallace article is copyright ACM and IEEE,
192and it may not be used for commercial purposes.
193
194A 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
196M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1.  This book provides
197good explanations and example C code for a multitude of compression methods
198including JPEG.  It is an excellent source if you are comfortable reading C
199code but don't know much about data compression in general.  The book's JPEG
200sample code is far from industrial-strength, but when you are ready to look
201at a full implementation, you've got one here...
202
203The best currently available description of JPEG is the textbook "JPEG Still
204Image Data Compression Standard" by William B. Pennebaker and Joan L.
205Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
206Price US$59.95, 638 pp.  The book includes the complete text of the ISO JPEG
207standards (DIS 10918-1 and draft DIS 10918-2).
208Although this is by far the most detailed and comprehensive exposition of
209JPEG publicly available, we point out that it is still missing an explanation
210of the most essential properties and algorithms of the underlying DCT
211technology.
212If you think that you know about DCT-based JPEG after reading this book,
213then you are in delusion.  The real fundamentals and corresponding potential
214of DCT-based JPEG are not publicly known so far, and that is the reason for
215all the mistaken developments taking place in the image coding domain.
216
217The original JPEG standard is divided into two parts, Part 1 being the actual
218specification, while Part 2 covers compliance testing methods.  Part 1 is
219titled "Digital Compression and Coding of Continuous-tone Still Images,
220Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
22110918-1, ITU-T T.81.  Part 2 is titled "Digital Compression and Coding of
222Continuous-tone Still Images, Part 2: Compliance testing" and has document
223numbers ISO/IEC IS 10918-2, ITU-T T.83.
224
225The JPEG standard does not specify all details of an interchangeable file
226format.  For the omitted details we follow the "JFIF" conventions, revision
2271.02.  A copy of the JFIF spec is available from:
228        Literature Department
229        C-Cube Microsystems, Inc.
230        1778 McCarthy Blvd.
231        Milpitas, CA 95035
232        phone (408) 944-6300,  fax (408) 944-6314
233A PostScript version of this document is available at
234http://www.ijg.org/files/jfif.ps.gz.  There is also a plain text version at
235http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures.
236
237The TIFF 6.0 file format specification can be obtained by FTP from
238ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz.  The JPEG incorporation scheme
239found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.
240IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).
241Instead, we recommend the JPEG design proposed by TIFF Technical Note #2
242(Compression tag 7).  Copies of this Note can be obtained from
243http://www.ijg.org/files/.  It is expected that the next revision
244of the TIFF spec will replace the 6.0 JPEG design with the Note's design.
245Although IJG's own code does not support TIFF/JPEG, the free libtiff library
246uses our library to implement TIFF/JPEG per the Note.
247
248
249ARCHIVE LOCATIONS
250=================
251
252The "official" archive site for this software is www.ijg.org.
253The most recent released version can always be found there in
254directory "files".  This particular version will be archived as
255http://www.ijg.org/files/jpegsrc.v7.tar.gz, and in Windows-compatible
256"zip" archive format as http://www.ijg.org/files/jpegsr7.zip.
257
258The JPEG FAQ (Frequently Asked Questions) article is a source of some
259general information about JPEG.
260It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/
261and other news.answers archive sites, including the official news.answers
262archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.
263If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu
264with body
265        send usenet/news.answers/jpeg-faq/part1
266        send usenet/news.answers/jpeg-faq/part2
267
268
269ACKNOWLEDGMENTS
270===============
271
272Thank to Juergen Bruder of the Georg-Cantor-Organization at the
273Martin-Luther-University Halle for providing me with a copy of the common
274DCT algorithm article, only to find out that I had come to the same result
275in a more direct and comprehensible way with a more generative approach.
276
277Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the
278ITU JPEG (Study Group 16) meeting in Geneva, Switzerland.
279
280Thank to Thomas Wiegand and Gary Sullivan for inviting me to the
281Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland.
282
283Thank to John Korejwa and Massimo Ballerini for inviting me to
284fruitful consultations in Boston, MA and Milan, Italy.
285
286Thank to Hendrik Elstner, Roland Fassauer, and Simone Zuck for
287corresponding business development.
288
289Thank to Nico Zschach and Dirk Stelling of the technical support team
290at the Digital Images company in Halle for providing me with extra
291equipment for configuration tests.
292
293Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful
294communication about JPEG configuration in Sigma Photo Pro software.
295
296Last but not least special thank to Thomas G. Lane for the original
297design and development of this singular software package.
298
299
300FILE FORMAT WARS
301================
302
303The ISO JPEG standards committee actually promotes different formats like
304JPEG-2000 or JPEG-XR which are incompatible with original DCT-based JPEG
305and which are based on faulty technologies.  IJG therefore does not and
306will not support such momentary mistakes (see REFERENCES).
307We have little or no sympathy for the promotion of these formats.  Indeed,
308one of the original reasons for developing this free software was to help
309force convergence on common, interoperable format standards for JPEG files.
310Don't use an incompatible file format!
311(In any case, our decoder will remain capable of reading existing JPEG
312image files indefinitely.)
313
314
315TO DO
316=====
317
318v7 is basically just a necessary interim release, paving the way for a
319major breakthrough in image coding technology with the next v8 package
320which is scheduled for release in the year 2010.
321
322Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.
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