1The Independent JPEG Group's JPEG software
2==========================================
3
4README for release 9 of 13-Jan-2013
5===================================
6
7This distribution contains the ninth 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 ISO/IEC JTC1/SC29/WG1 standards committee
17(also known as JPEG, together with ITU-T SG16).
18
19
20DOCUMENTATION ROADMAP
21=====================
22
23This file contains the following sections:
24
25OVERVIEW General description of JPEG and the IJG software.
26LEGAL ISSUES Copyright, lack of warranty, terms of distribution.
27REFERENCES Where to learn more about JPEG.
28ARCHIVE LOCATIONS Where to find newer versions of this software.
29ACKNOWLEDGMENTS Special thanks.
30FILE FORMAT WARS Software *not* to get.
31TO DO Plans for future IJG releases.
32
33Other documentation files in the distribution are:
34
35User documentation:
36 install.txt How to configure and install the IJG software.
37 usage.txt Usage instructions for cjpeg, djpeg, jpegtran,
38 rdjpgcom, and wrjpgcom.
39 *.1 Unix-style man pages for programs (same info as usage.txt).
40 wizard.txt Advanced usage instructions for JPEG wizards only.
41 change.log Version-to-version change highlights.
42Programmer and internal documentation:
43 libjpeg.txt How to use the JPEG library in your own programs.
44 example.c Sample code for calling the JPEG library.
45 structure.txt Overview of the JPEG library's internal structure.
46 filelist.txt Road map of IJG files.
47 coderules.txt Coding style rules --- please read if you contribute code.
48
49Please read at least the files install.txt and usage.txt. Some information
50can also be found in the JPEG FAQ (Frequently Asked Questions) article. See
51ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.
52
53If you want to understand how the JPEG code works, we suggest reading one or
54more of the REFERENCES, then looking at the documentation files (in roughly
55the order listed) before diving into the code.
56
57
58OVERVIEW
59========
60
61This package contains C software to implement JPEG image encoding, decoding,
62and transcoding. JPEG (pronounced "jay-peg") is a standardized compression
63method for full-color and gray-scale images.
64
65This software implements JPEG baseline, extended-sequential, and progressive
66compression processes. Provision is made for supporting all variants of these
67processes, although some uncommon parameter settings aren't implemented yet.
68We have made no provision for supporting the hierarchical or lossless
69processes defined in the standard.
70
71We provide a set of library routines for reading and writing JPEG image files,
72plus two sample applications "cjpeg" and "djpeg", which use the library to
73perform conversion between JPEG and some other popular image file formats.
74The library is intended to be reused in other applications.
75
76In order to support file conversion and viewing software, we have included
77considerable functionality beyond the bare JPEG coding/decoding capability;
78for example, the color quantization modules are not strictly part of JPEG
79decoding, but they are essential for output to colormapped file formats or
80colormapped displays. These extra functions can be compiled out of the
81library if not required for a particular application.
82
83We have also included "jpegtran", a utility for lossless transcoding between
84different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple
85applications for inserting and extracting textual comments in JFIF files.
86
87The emphasis in designing this software has been on achieving portability and
88flexibility, while also making it fast enough to be useful. In particular,
89the software is not intended to be read as a tutorial on JPEG. (See the
90REFERENCES section for introductory material.) Rather, it is intended to
91be reliable, portable, industrial-strength code. We do not claim to have
92achieved that goal in every aspect of the software, but we strive for it.
93
94We welcome the use of this software as a component of commercial products.
95No royalty is required, but we do ask for an acknowledgement in product
96documentation, as described under LEGAL ISSUES.
97
98
99LEGAL ISSUES
100============
101
102In plain English:
103
1041. We don't promise that this software works. (But if you find any bugs,
105 please let us know!)
1062. You can use this software for whatever you want. You don't have to pay us.
1073. You may not pretend that you wrote this software. If you use it in a
108 program, you must acknowledge somewhere in your documentation that
109 you've used the IJG code.
110
111In legalese:
112
113The authors make NO WARRANTY or representation, either express or implied,
114with respect to this software, its quality, accuracy, merchantability, or
115fitness for a particular purpose. This software is provided "AS IS", and you,
116its user, assume the entire risk as to its quality and accuracy.
117
118This software is copyright (C) 1991-2013, Thomas G. Lane, Guido Vollbeding.
119All Rights Reserved except as specified below.
120
121Permission is hereby granted to use, copy, modify, and distribute this
122software (or portions thereof) for any purpose, without fee, subject to these
123conditions:
124(1) If any part of the source code for this software is distributed, then this
125README file must be included, with this copyright and no-warranty notice
126unaltered; and any additions, deletions, or changes to the original files
127must be clearly indicated in accompanying documentation.
128(2) If only executable code is distributed, then the accompanying
129documentation must state that "this software is based in part on the work of
130the Independent JPEG Group".
131(3) Permission for use of this software is granted only if the user accepts
132full responsibility for any undesirable consequences; the authors accept
133NO LIABILITY for damages of any kind.
134
135These conditions apply to any software derived from or based on the IJG code,
136not just to the unmodified library. If you use our work, you ought to
137acknowledge us.
138
139Permission is NOT granted for the use of any IJG author's name or company name
140in advertising or publicity relating to this software or products derived from
141it. This software may be referred to only as "the Independent JPEG Group's
142software".
143
144We specifically permit and encourage the use of this software as the basis of
145commercial products, provided that all warranty or liability claims are
146assumed by the product vendor.
147
148
149The Unix configuration script "configure" was produced with GNU Autoconf.
150It is copyright by the Free Software Foundation but is freely distributable.
151The same holds for its supporting scripts (config.guess, config.sub,
152ltmain.sh). Another support script, install-sh, is copyright by X Consortium
153but is also freely distributable.
154
155The IJG distribution formerly included code to read and write GIF files.
156To avoid entanglement with the Unisys LZW patent, GIF reading support has
157been removed altogether, and the GIF writer has been simplified to produce
158"uncompressed GIFs". This technique does not use the LZW algorithm; the
159resulting GIF files are larger than usual, but are readable by all standard
160GIF decoders.
161
162We are required to state that
163 "The Graphics Interchange Format(c) is the Copyright property of
164 CompuServe Incorporated. GIF(sm) is a Service Mark property of
165 CompuServe Incorporated."
166
167
168REFERENCES
169==========
170
171We recommend reading one or more of these references before trying to
172understand the innards of the JPEG software.
173
174The best short technical introduction to the JPEG compression algorithm is
175 Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
176 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
177(Adjacent articles in that issue discuss MPEG motion picture compression,
178applications of JPEG, and related topics.) If you don't have the CACM issue
179handy, a PostScript file containing a revised version of Wallace's article is
180available at http://www.ijg.org/files/wallace.ps.gz. The file (actually
181a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
182omits the sample images that appeared in CACM, but it includes corrections
183and some added material. Note: the Wallace article is copyright ACM and IEEE,
184and it may not be used for commercial purposes.
185
186A somewhat less technical, more leisurely introduction to JPEG can be found in
187"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by
188M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides
189good explanations and example C code for a multitude of compression methods
190including JPEG. It is an excellent source if you are comfortable reading C
191code but don't know much about data compression in general. The book's JPEG
192sample code is far from industrial-strength, but when you are ready to look
193at a full implementation, you've got one here...
194
195The best currently available description of JPEG is the textbook "JPEG Still
196Image Data Compression Standard" by William B. Pennebaker and Joan L.
197Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
198Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG
199standards (DIS 10918-1 and draft DIS 10918-2).
200Although this is by far the most detailed and comprehensive exposition of
201JPEG publicly available, we point out that it is still missing an explanation
202of the most essential properties and algorithms of the underlying DCT
203technology.
204If you think that you know about DCT-based JPEG after reading this book,
205then you are in delusion. The real fundamentals and corresponding potential
206of DCT-based JPEG are not publicly known so far, and that is the reason for
207all the mistaken developments taking place in the image coding domain.
208
209The original JPEG standard is divided into two parts, Part 1 being the actual
210specification, while Part 2 covers compliance testing methods. Part 1 is
211titled "Digital Compression and Coding of Continuous-tone Still Images,
212Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
21310918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of
214Continuous-tone Still Images, Part 2: Compliance testing" and has document
215numbers ISO/IEC IS 10918-2, ITU-T T.83.
216IJG JPEG 8 introduced an implementation of the JPEG SmartScale extension
217which is specified in two documents: A contributed document at ITU and ISO
218with title "ITU-T JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced
219Image Coding", April 2006, Geneva, Switzerland. The latest version of this
220document is Revision 3. And a contributed document ISO/IEC JTC1/SC29/WG1 N
2215799 with title "Evolution of JPEG", June/July 2011, Berlin, Germany.
222IJG JPEG 9 introduces a reversible color transform for improved lossless
223compression which is described in a contributed document ISO/IEC JTC1/SC29/
224WG1 N 6080 with title "JPEG 9 Lossless Coding", June/July 2012, Paris,
225France.
226
227The JPEG standard does not specify all details of an interchangeable file
228format. For the omitted details we follow the "JFIF" conventions, revision
2291.02. JFIF 1.02 has been adopted as an Ecma International Technical Report
230and thus received a formal publication status. It is available as a free
231download in PDF format from
232http://www.ecma-international.org/publications/techreports/E-TR-098.htm.
233A PostScript version of the JFIF 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.v9.tar.gz, and in Windows-compatible
256"zip" archive format as http://www.ijg.org/files/jpegsr9.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 for providing me with a copy of the common DCT
273algorithm article, only to find out that I had come to the same result
274in a more direct and comprehensible way with a more generative approach.
275
276Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the
277ITU JPEG (Study Group 16) meeting in Geneva, Switzerland.
278
279Thank to Thomas Wiegand and Gary Sullivan for inviting me to the
280Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland.
281
282Thank to Thomas Richter and Daniel Lee for inviting me to the
283ISO/IEC JTC1/SC29/WG1 (also known as JPEG, together with ITU-T SG16)
284meeting in Berlin, Germany.
285
286Thank to John Korejwa and Massimo Ballerini for inviting me to
287fruitful consultations in Boston, MA and Milan, Italy.
288
289Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther
290Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel
291for corresponding business development.
292
293Thank to Nico Zschach and Dirk Stelling of the technical support team
294at the Digital Images company in Halle for providing me with extra
295equipment for configuration tests.
296
297Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful
298communication about JPEG configuration in Sigma Photo Pro software.
299
300Thank to Andrew Finkenstadt for hosting the ijg.org site.
301
302Last but not least special thank to Thomas G. Lane for the original
303design and development of this singular software package.
304
305
306FILE FORMAT WARS
307================
308
309The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together
310with ITU-T SG16) currently promotes different formats containing the name
311"JPEG" which is misleading because these formats are incompatible with
312original DCT-based JPEG and are based on faulty technologies.
313IJG therefore does not and will not support such momentary mistakes
314(see REFERENCES).
315There exist also distributions under the name "OpenJPEG" promoting such
316kind of formats which is misleading because they don't support original
317JPEG images.
318We have no sympathy for the promotion of inferior formats. Indeed, one of
319the original reasons for developing this free software was to help force
320convergence on common, interoperable format standards for JPEG files.
321Don't use an incompatible file format!
322(In any case, our decoder will remain capable of reading existing JPEG
323image files indefinitely.)
324
325Furthermore, the ISO committee pretends to be "responsible for the popular
326JPEG" in their public reports which is not true because they don't respond to
327actual requirements for the maintenance of the original JPEG specification.
328
329There are currently different distributions in circulation containing the
330name "libjpeg" which is misleading because they don't have the features and
331are incompatible with formats supported by actual IJG libjpeg distributions.
332One of those fakes is released by members of the ISO committee and just uses
333the name of libjpeg for misdirection of people, similar to the abuse of the
334name JPEG as described above, while having nothing in common with actual IJG
335libjpeg distributions.
336The other one claims to be a "derivative" or "fork" of the original libjpeg
337and violates the license conditions as described under LEGAL ISSUES above.
338We have no sympathy for the release of misleading and illegal distributions
339derived from obsolete code bases.
340Don't use an obsolete code base!
341
342
343TO DO
344=====
345
346Version 9 is the second release of a new generation JPEG standard
347to overcome the limitations of the original JPEG specification.
348More features are being prepared for coming releases...
349
350Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.
351