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/src/FreeImage/Source/LibJPEG/README

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  1The Independent JPEG Group's JPEG software
  2==========================================
  3
  4README for release 8d of 15-Jan-2012
  5====================================
  6
  7This distribution contains the eighth 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) 1991-2012, 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
149ansi2knr.c is included in this distribution by permission of L. Peter Deutsch,
150sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA.
151ansi2knr.c is NOT covered by the above copyright and conditions, but instead
152by the usual distribution terms of the Free Software Foundation; principally,
153that you must include source code if you redistribute it.  (See the file
154ansi2knr.c for full details.)  However, since ansi2knr.c is not needed as part
155of any program generated from the IJG code, this does not limit you more than
156the foregoing paragraphs do.
157
158The Unix configuration script "configure" was produced with GNU Autoconf.
159It is copyright by the Free Software Foundation but is freely distributable.
160The same holds for its supporting scripts (config.guess, config.sub,
161ltmain.sh).  Another support script, install-sh, is copyright by X Consortium
162but is also freely distributable.
163
164The IJG distribution formerly included code to read and write GIF files.
165To avoid entanglement with the Unisys LZW patent, GIF reading support has
166been removed altogether, and the GIF writer has been simplified to produce
167"uncompressed GIFs".  This technique does not use the LZW algorithm; the
168resulting GIF files are larger than usual, but are readable by all standard
169GIF decoders.
170
171We are required to state that
172    "The Graphics Interchange Format(c) is the Copyright property of
173    CompuServe Incorporated.  GIF(sm) is a Service Mark property of
174    CompuServe Incorporated."
175
176
177REFERENCES
178==========
179
180We recommend reading one or more of these references before trying to
181understand the innards of the JPEG software.
182
183The best short technical introduction to the JPEG compression algorithm is
184	Wallace, Gregory K.  "The JPEG Still Picture Compression Standard",
185	Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
186(Adjacent articles in that issue discuss MPEG motion picture compression,
187applications of JPEG, and related topics.)  If you don't have the CACM issue
188handy, a PostScript file containing a revised version of Wallace's article is
189available at http://www.ijg.org/files/wallace.ps.gz.  The file (actually
190a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
191omits the sample images that appeared in CACM, but it includes corrections
192and some added material.  Note: the Wallace article is copyright ACM and IEEE,
193and it may not be used for commercial purposes.
194
195A somewhat less technical, more leisurely introduction to JPEG can be found in
196"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by
197M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1.  This book provides
198good explanations and example C code for a multitude of compression methods
199including JPEG.  It is an excellent source if you are comfortable reading C
200code but don't know much about data compression in general.  The book's JPEG
201sample code is far from industrial-strength, but when you are ready to look
202at a full implementation, you've got one here...
203
204The best currently available description of JPEG is the textbook "JPEG Still
205Image Data Compression Standard" by William B. Pennebaker and Joan L.
206Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
207Price US$59.95, 638 pp.  The book includes the complete text of the ISO JPEG
208standards (DIS 10918-1 and draft DIS 10918-2).
209Although this is by far the most detailed and comprehensive exposition of
210JPEG publicly available, we point out that it is still missing an explanation
211of the most essential properties and algorithms of the underlying DCT
212technology.
213If you think that you know about DCT-based JPEG after reading this book,
214then you are in delusion.  The real fundamentals and corresponding potential
215of DCT-based JPEG are not publicly known so far, and that is the reason for
216all the mistaken developments taking place in the image coding domain.
217
218The original JPEG standard is divided into two parts, Part 1 being the actual
219specification, while Part 2 covers compliance testing methods.  Part 1 is
220titled "Digital Compression and Coding of Continuous-tone Still Images,
221Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
22210918-1, ITU-T T.81.  Part 2 is titled "Digital Compression and Coding of
223Continuous-tone Still Images, Part 2: Compliance testing" and has document
224numbers ISO/IEC IS 10918-2, ITU-T T.83.
225IJG JPEG 8 introduces an implementation of the JPEG SmartScale extension
226which is specified in two documents:  A contributed document at ITU and ISO
227with title "ITU-T JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced
228Image Coding", April 2006, Geneva, Switzerland.  The latest version of this
229document is Revision 3.  And a contributed document ISO/IEC JTC1/SC29/WG1 N
2305799 with title "Evolution of JPEG", June/July 2011, Berlin, Germany.
231
232The JPEG standard does not specify all details of an interchangeable file
233format.  For the omitted details we follow the "JFIF" conventions, revision
2341.02.  JFIF 1.02 has been adopted as an Ecma International Technical Report
235and thus received a formal publication status.  It is available as a free
236download in PDF format from
237http://www.ecma-international.org/publications/techreports/E-TR-098.htm.
238A PostScript version of the JFIF document is available at
239http://www.ijg.org/files/jfif.ps.gz.  There is also a plain text version at
240http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures.
241
242The TIFF 6.0 file format specification can be obtained by FTP from
243ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz.  The JPEG incorporation scheme
244found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.
245IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).
246Instead, we recommend the JPEG design proposed by TIFF Technical Note #2
247(Compression tag 7).  Copies of this Note can be obtained from
248http://www.ijg.org/files/.  It is expected that the next revision
249of the TIFF spec will replace the 6.0 JPEG design with the Note's design.
250Although IJG's own code does not support TIFF/JPEG, the free libtiff library
251uses our library to implement TIFF/JPEG per the Note.
252
253
254ARCHIVE LOCATIONS
255=================
256
257The "official" archive site for this software is www.ijg.org.
258The most recent released version can always be found there in
259directory "files".  This particular version will be archived as
260http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible
261"zip" archive format as http://www.ijg.org/files/jpegsr8d.zip.
262
263The JPEG FAQ (Frequently Asked Questions) article is a source of some
264general information about JPEG.
265It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/
266and other news.answers archive sites, including the official news.answers
267archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.
268If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu
269with body
270	send usenet/news.answers/jpeg-faq/part1
271	send usenet/news.answers/jpeg-faq/part2
272
273
274ACKNOWLEDGMENTS
275===============
276
277Thank to Juergen Bruder for providing me with a copy of the common DCT
278algorithm article, only to find out that I had come to the same result
279in a more direct and comprehensible way with a more generative approach.
280
281Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the
282ITU JPEG (Study Group 16) meeting in Geneva, Switzerland.
283
284Thank to Thomas Wiegand and Gary Sullivan for inviting me to the
285Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland.
286
287Thank to Thomas Richter and Daniel Lee for inviting me to the
288ISO/IEC JTC1/SC29/WG1 (also known as JPEG, together with ITU-T SG16)
289meeting in Berlin, Germany.
290
291Thank to John Korejwa and Massimo Ballerini for inviting me to
292fruitful consultations in Boston, MA and Milan, Italy.
293
294Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther
295Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel
296for corresponding business development.
297
298Thank to Nico Zschach and Dirk Stelling of the technical support team
299at the Digital Images company in Halle for providing me with extra
300equipment for configuration tests.
301
302Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful
303communication about JPEG configuration in Sigma Photo Pro software.
304
305Thank to Andrew Finkenstadt for hosting the ijg.org site.
306
307Last but not least special thank to Thomas G. Lane for the original
308design and development of this singular software package.
309
310
311FILE FORMAT WARS
312================
313
314The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together
315with ITU-T SG16) currently promotes different formats containing the name
316"JPEG" which is misleading because these formats are incompatible with
317original DCT-based JPEG and are based on faulty technologies.
318IJG therefore does not and will not support such momentary mistakes
319(see REFERENCES).
320There exist also distributions under the name "OpenJPEG" promoting such
321kind of formats which is misleading because they don't support original
322JPEG images.
323We have no sympathy for the promotion of inferior formats.  Indeed, one of
324the original reasons for developing this free software was to help force
325convergence on common, interoperable format standards for JPEG files.
326Don't use an incompatible file format!
327(In any case, our decoder will remain capable of reading existing JPEG
328image files indefinitely.)
329
330Furthermore, the ISO committee pretends to be "responsible for the popular
331JPEG" in their public reports which is not true because they don't respond to
332actual requirements for the maintenance of the original JPEG specification.
333
334There are currently distributions in circulation containing the name
335"libjpeg" which claim to be a "derivative" or "fork" of the original
336libjpeg, but don't have the features and are incompatible with formats
337supported by actual IJG libjpeg distributions.  Furthermore, they
338violate the license conditions as described under LEGAL ISSUES above.
339We have no sympathy for the release of misleading and illegal
340distributions derived from obsolete code bases.
341Don't use an obsolete code base!
342
343
344TO DO
345=====
346
347Version 8 is the first release of a new generation JPEG standard
348to overcome the limitations of the original JPEG specification.
349More features are being prepared for coming releases...
350
351Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.