379 lines
18 KiB
Plaintext
379 lines
18 KiB
Plaintext
The Independent JPEG Group's JPEG software
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==========================================
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README for release 9c of 14-Jan-2018
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====================================
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This distribution contains the ninth public release of the Independent JPEG
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Group's free JPEG software. You are welcome to redistribute this software and
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to use it for any purpose, subject to the conditions under LEGAL ISSUES, below.
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This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone,
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Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson,
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Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers,
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and other members of the Independent JPEG Group.
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IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee
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(previously known as JPEG, together with ITU-T SG16).
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DOCUMENTATION ROADMAP
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=====================
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This file contains the following sections:
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OVERVIEW General description of JPEG and the IJG software.
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LEGAL ISSUES Copyright, lack of warranty, terms of distribution.
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REFERENCES Where to learn more about JPEG.
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ARCHIVE LOCATIONS Where to find newer versions of this software.
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ACKNOWLEDGMENTS Special thanks.
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FILE FORMAT WARS Software *not* to get.
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TO DO Plans for future IJG releases.
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Other documentation files in the distribution are:
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User documentation:
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install.txt How to configure and install the IJG software.
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usage.txt Usage instructions for cjpeg, djpeg, jpegtran,
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rdjpgcom, and wrjpgcom.
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*.1 Unix-style man pages for programs (same info as usage.txt).
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wizard.txt Advanced usage instructions for JPEG wizards only.
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change.log Version-to-version change highlights.
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Programmer and internal documentation:
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libjpeg.txt How to use the JPEG library in your own programs.
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example.c Sample code for calling the JPEG library.
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structure.txt Overview of the JPEG library's internal structure.
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filelist.txt Road map of IJG files.
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coderules.txt Coding style rules --- please read if you contribute code.
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Please read at least the files install.txt and usage.txt. Some information
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can also be found in the JPEG FAQ (Frequently Asked Questions) article. See
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ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.
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If you want to understand how the JPEG code works, we suggest reading one or
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more of the REFERENCES, then looking at the documentation files (in roughly
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the order listed) before diving into the code.
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OVERVIEW
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========
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This package contains C software to implement JPEG image encoding, decoding,
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and transcoding. JPEG (pronounced "jay-peg") is a standardized compression
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method for full-color and grayscale images.
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This software implements JPEG baseline, extended-sequential, and progressive
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compression processes. Provision is made for supporting all variants of these
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processes, although some uncommon parameter settings aren't implemented yet.
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We have made no provision for supporting the hierarchical or lossless
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processes defined in the standard.
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We provide a set of library routines for reading and writing JPEG image files,
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plus two sample applications "cjpeg" and "djpeg", which use the library to
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perform conversion between JPEG and some other popular image file formats.
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The library is intended to be reused in other applications.
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In order to support file conversion and viewing software, we have included
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considerable functionality beyond the bare JPEG coding/decoding capability;
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for example, the color quantization modules are not strictly part of JPEG
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decoding, but they are essential for output to colormapped file formats or
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colormapped displays. These extra functions can be compiled out of the
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library if not required for a particular application.
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We have also included "jpegtran", a utility for lossless transcoding between
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different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple
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applications for inserting and extracting textual comments in JFIF files.
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The emphasis in designing this software has been on achieving portability and
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flexibility, while also making it fast enough to be useful. In particular,
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the software is not intended to be read as a tutorial on JPEG. (See the
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REFERENCES section for introductory material.) Rather, it is intended to
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be reliable, portable, industrial-strength code. We do not claim to have
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achieved that goal in every aspect of the software, but we strive for it.
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We welcome the use of this software as a component of commercial products.
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No royalty is required, but we do ask for an acknowledgement in product
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documentation, as described under LEGAL ISSUES.
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LEGAL ISSUES
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============
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In plain English:
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1. We don't promise that this software works. (But if you find any bugs,
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please let us know!)
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2. You can use this software for whatever you want. You don't have to pay us.
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3. You may not pretend that you wrote this software. If you use it in a
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program, you must acknowledge somewhere in your documentation that
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you've used the IJG code.
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In legalese:
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The authors make NO WARRANTY or representation, either express or implied,
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with respect to this software, its quality, accuracy, merchantability, or
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fitness for a particular purpose. This software is provided "AS IS", and you,
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its user, assume the entire risk as to its quality and accuracy.
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This software is copyright (C) 1991-2018, Thomas G. Lane, Guido Vollbeding.
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All Rights Reserved except as specified below.
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Permission is hereby granted to use, copy, modify, and distribute this
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software (or portions thereof) for any purpose, without fee, subject to these
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conditions:
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(1) If any part of the source code for this software is distributed, then this
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README file must be included, with this copyright and no-warranty notice
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unaltered; and any additions, deletions, or changes to the original files
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must be clearly indicated in accompanying documentation.
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(2) If only executable code is distributed, then the accompanying
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documentation must state that "this software is based in part on the work of
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the Independent JPEG Group".
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(3) Permission for use of this software is granted only if the user accepts
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full responsibility for any undesirable consequences; the authors accept
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NO LIABILITY for damages of any kind.
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These conditions apply to any software derived from or based on the IJG code,
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not just to the unmodified library. If you use our work, you ought to
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acknowledge us.
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Permission is NOT granted for the use of any IJG author's name or company name
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in advertising or publicity relating to this software or products derived from
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it. This software may be referred to only as "the Independent JPEG Group's
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software".
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We specifically permit and encourage the use of this software as the basis of
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commercial products, provided that all warranty or liability claims are
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assumed by the product vendor.
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The Unix configuration script "configure" was produced with GNU Autoconf.
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It is copyright by the Free Software Foundation but is freely distributable.
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The same holds for its supporting scripts (config.guess, config.sub,
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ltmain.sh). Another support script, install-sh, is copyright by X Consortium
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but is also freely distributable.
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The IJG distribution formerly included code to read and write GIF files.
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To avoid entanglement with the Unisys LZW patent (now expired), GIF reading
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support has been removed altogether, and the GIF writer has been simplified
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to produce "uncompressed GIFs". This technique does not use the LZW
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algorithm; the resulting GIF files are larger than usual, but are readable
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by all standard GIF decoders.
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REFERENCES
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==========
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We recommend reading one or more of these references before trying to
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understand the innards of the JPEG software.
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The best short technical introduction to the JPEG compression algorithm is
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Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
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Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
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(Adjacent articles in that issue discuss MPEG motion picture compression,
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applications of JPEG, and related topics.) If you don't have the CACM issue
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handy, a PDF file containing a revised version of Wallace's article is
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available at http://www.ijg.org/files/Wallace.JPEG.pdf. The file (actually
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a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
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omits the sample images that appeared in CACM, but it includes corrections
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and some added material. Note: the Wallace article is copyright ACM and IEEE,
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and it may not be used for commercial purposes.
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A somewhat less technical, more leisurely introduction to JPEG can be found in
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"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by
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M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides
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good explanations and example C code for a multitude of compression methods
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including JPEG. It is an excellent source if you are comfortable reading C
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code but don't know much about data compression in general. The book's JPEG
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sample code is far from industrial-strength, but when you are ready to look
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at a full implementation, you've got one here...
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The best currently available description of JPEG is the textbook "JPEG Still
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Image Data Compression Standard" by William B. Pennebaker and Joan L.
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Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
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Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG
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standards (DIS 10918-1 and draft DIS 10918-2).
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Although this is by far the most detailed and comprehensive exposition of
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JPEG publicly available, we point out that it is still missing an explanation
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of the most essential properties and algorithms of the underlying DCT
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technology.
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If you think that you know about DCT-based JPEG after reading this book,
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then you are in delusion. The real fundamentals and corresponding potential
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of DCT-based JPEG are not publicly known so far, and that is the reason for
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all the mistaken developments taking place in the image coding domain.
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The original JPEG standard is divided into two parts, Part 1 being the actual
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specification, while Part 2 covers compliance testing methods. Part 1 is
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titled "Digital Compression and Coding of Continuous-tone Still Images,
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Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
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10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of
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Continuous-tone Still Images, Part 2: Compliance testing" and has document
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numbers ISO/IEC IS 10918-2, ITU-T T.83.
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IJG JPEG 8 introduced an implementation of the JPEG SmartScale extension
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which is specified in two documents: A contributed document at ITU and ISO
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with title "ITU-T JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced
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Image Coding", April 2006, Geneva, Switzerland. The latest version of this
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document is Revision 3. And a contributed document ISO/IEC JTC1/SC29/WG1 N
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5799 with title "Evolution of JPEG", June/July 2011, Berlin, Germany.
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IJG JPEG 9 introduces a reversible color transform for improved lossless
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compression which is described in a contributed document ISO/IEC JTC1/SC29/
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WG1 N 6080 with title "JPEG 9 Lossless Coding", June/July 2012, Paris,
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France.
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The JPEG standard does not specify all details of an interchangeable file
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format. For the omitted details we follow the "JFIF" conventions, version 2.
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JFIF version 1 has been adopted as Recommendation ITU-T T.871 (05/2011) :
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Information technology - Digital compression and coding of continuous-tone
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still images: JPEG File Interchange Format (JFIF). It is available as a
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free download in PDF file format from http://www.itu.int/rec/T-REC-T.871.
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A PDF file of the older JFIF document is available at
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http://www.w3.org/Graphics/JPEG/jfif3.pdf.
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The TIFF 6.0 file format specification can be obtained by FTP from
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ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme
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found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.
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IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).
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Instead, we recommend the JPEG design proposed by TIFF Technical Note #2
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(Compression tag 7). Copies of this Note can be obtained from
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http://www.ijg.org/files/. It is expected that the next revision
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of the TIFF spec will replace the 6.0 JPEG design with the Note's design.
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Although IJG's own code does not support TIFF/JPEG, the free libtiff library
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uses our library to implement TIFF/JPEG per the Note.
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ARCHIVE LOCATIONS
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=================
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The "official" archive site for this software is www.ijg.org.
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The most recent released version can always be found there in
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directory "files". This particular version will be archived as
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http://www.ijg.org/files/jpegsrc.v9c.tar.gz, and in Windows-compatible
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"zip" archive format as http://www.ijg.org/files/jpegsr9c.zip.
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The JPEG FAQ (Frequently Asked Questions) article is a source of some
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general information about JPEG.
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It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/
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and other news.answers archive sites, including the official news.answers
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archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.
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If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu
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with body
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send usenet/news.answers/jpeg-faq/part1
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send usenet/news.answers/jpeg-faq/part2
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ACKNOWLEDGMENTS
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===============
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Thank to Juergen Bruder for providing me with a copy of the common DCT
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algorithm article, only to find out that I had come to the same result
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in a more direct and comprehensible way with a more generative approach.
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Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the
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ITU JPEG (Study Group 16) meeting in Geneva, Switzerland.
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Thank to Thomas Wiegand and Gary Sullivan for inviting me to the
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Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland.
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Thank to Thomas Richter and Daniel Lee for inviting me to the
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ISO/IEC JTC1/SC29/WG1 (previously known as JPEG, together with ITU-T SG16)
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meeting in Berlin, Germany.
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Thank to John Korejwa and Massimo Ballerini for inviting me to
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fruitful consultations in Boston, MA and Milan, Italy.
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Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther
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Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel
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for corresponding business development.
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Thank to Nico Zschach and Dirk Stelling of the technical support team
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at the Digital Images company in Halle for providing me with extra
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equipment for configuration tests.
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Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful
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communication about JPEG configuration in Sigma Photo Pro software.
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Thank to Andrew Finkenstadt for hosting the ijg.org site.
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Thank to Thomas G. Lane for the original design and development of
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this singular software package.
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Thank to Lars Goehler, Andreas Heinecke, Sebastian Fuss, Yvonne Roebert,
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Andrej Werner, and Ulf-Dietrich Braumann for support and public relations.
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FILE FORMAT WARS
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The ISO/IEC JTC1/SC29/WG1 standards committee (previously known as JPEG,
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together with ITU-T SG16) currently promotes different formats containing
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the name "JPEG" which is misleading because these formats are incompatible
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with original DCT-based JPEG and are based on faulty technologies.
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IJG therefore does not and will not support such momentary mistakes
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(see REFERENCES).
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There exist also distributions under the name "OpenJPEG" promoting such
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kind of formats which is misleading because they don't support original
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JPEG images.
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We have no sympathy for the promotion of inferior formats. Indeed, one of
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the original reasons for developing this free software was to help force
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convergence on common, interoperable format standards for JPEG files.
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Don't use an incompatible file format!
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(In any case, our decoder will remain capable of reading existing JPEG
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image files indefinitely.)
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The ISO committee pretends to be "responsible for the popular JPEG" in their
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public reports which is not true because they don't respond to actual
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requirements for the maintenance of the original JPEG specification.
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Furthermore, the ISO committee pretends to "ensure interoperability" with
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their standards which is not true because their "standards" support only
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application-specific and proprietary use cases and contain mathematically
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incorrect code.
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There are currently different distributions in circulation containing the
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name "libjpeg" which is misleading because they don't have the features and
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are incompatible with formats supported by actual IJG libjpeg distributions.
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One of those fakes is released by members of the ISO committee and just uses
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the name of libjpeg for misdirection of people, similar to the abuse of the
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name JPEG as described above, while having nothing in common with actual IJG
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libjpeg distributions and containing mathematically incorrect code.
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The other one claims to be a "derivative" or "fork" of the original libjpeg,
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but violates the license conditions as described under LEGAL ISSUES above
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and violates basic C programming properties.
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We have no sympathy for the release of misleading, incorrect and illegal
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distributions derived from obsolete code bases.
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Don't use an obsolete code base!
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According to the UCC (Uniform Commercial Code) law, IJG has the lawful and
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legal right to foreclose on certain standardization bodies and other
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institutions or corporations that knowingly perform substantial and
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systematic deceptive acts and practices, fraud, theft, and damaging of the
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value of the people of this planet without their knowing, willing and
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intentional consent.
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The titles, ownership, and rights of these institutions and all their assets
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are now duly secured and held in trust for the free people of this planet.
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People of the planet, on every country, may have a financial interest in
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the assets of these former principals, agents, and beneficiaries of the
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foreclosed institutions and corporations.
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IJG asserts what is: that each man, woman, and child has unalienable value
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and rights granted and deposited in them by the Creator and not any one of
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the people is subordinate to any artificial principality, corporate fiction
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or the special interest of another without their appropriate knowing,
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willing and intentional consent made by contract or accommodation agreement.
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IJG expresses that which already was.
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The people have already determined and demanded that public administration
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entities, national governments, and their supporting judicial systems must
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be fully transparent, accountable, and liable.
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IJG has secured the value for all concerned free people of the planet.
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A partial list of foreclosed institutions and corporations ("Hall of Shame")
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is currently prepared and will be published later.
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TO DO
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=====
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Version 9 is the second release of a new generation JPEG standard
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to overcome the limitations of the original JPEG specification,
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and is the first true source reference JPEG codec.
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More features are being prepared for coming releases...
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Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.
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