The Independent JPEG Group's JPEG software

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README for release 9 of 13-Jan-2013

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This distribution contains the ninth public release of the Independent JPEG

Group's free JPEG software.  You are welcome to redistribute this software and

to use it for any purpose, subject to the conditions under LEGAL ISSUES, below.

This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone,

Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson,

Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers,

and other members of the Independent JPEG Group.

IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee

(also known as JPEG, together with ITU-T SG16).

DOCUMENTATION ROADMAP

=====================

This file contains the following sections:

OVERVIEW            General description of JPEG and the IJG software.

LEGAL ISSUES        Copyright, lack of warranty, terms of distribution.

REFERENCES          Where to learn more about JPEG.

ARCHIVE LOCATIONS   Where to find newer versions of this software.

ACKNOWLEDGMENTS     Special thanks.

FILE FORMAT WARS    Software *not* to get.

TO DO               Plans for future IJG releases.

Other documentation files in the distribution are:

User documentation:

  install.txt       How to configure and install the IJG software.

  usage.txt         Usage instructions for cjpeg, djpeg, jpegtran,

                    rdjpgcom, and wrjpgcom.

  *.1               Unix-style man pages for programs (same info as usage.txt).

  wizard.txt        Advanced usage instructions for JPEG wizards only.

  change.log        Version-to-version change highlights.

Programmer and internal documentation:

  libjpeg.txt       How to use the JPEG library in your own programs.

  example.c         Sample code for calling the JPEG library.

  structure.txt     Overview of the JPEG library's internal structure.

  filelist.txt      Road map of IJG files.

  coderules.txt     Coding style rules --- please read if you contribute code.

Please read at least the files install.txt and usage.txt.  Some information

can also be found in the JPEG FAQ (Frequently Asked Questions) article.  See

ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.

If you want to understand how the JPEG code works, we suggest reading one or

more of the REFERENCES, then looking at the documentation files (in roughly

the order listed) before diving into the code.

OVERVIEW

========

This package contains C software to implement JPEG image encoding, decoding,

and transcoding.  JPEG (pronounced "jay-peg") is a standardized compression

method for full-color and gray-scale images.

This software implements JPEG baseline, extended-sequential, and progressive

compression processes.  Provision is made for supporting all variants of these

processes, although some uncommon parameter settings aren't implemented yet.

We have made no provision for supporting the hierarchical or lossless

processes defined in the standard.

We provide a set of library routines for reading and writing JPEG image files,

plus two sample applications "cjpeg" and "djpeg", which use the library to

perform conversion between JPEG and some other popular image file formats.

The library is intended to be reused in other applications.

In order to support file conversion and viewing software, we have included

considerable functionality beyond the bare JPEG coding/decoding capability;

for example, the color quantization modules are not strictly part of JPEG

decoding, but they are essential for output to colormapped file formats or

colormapped displays.  These extra functions can be compiled out of the

library if not required for a particular application.

We have also included "jpegtran", a utility for lossless transcoding between

different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple

applications for inserting and extracting textual comments in JFIF files.

The emphasis in designing this software has been on achieving portability and

flexibility, while also making it fast enough to be useful.  In particular,

the software is not intended to be read as a tutorial on JPEG.  (See the

REFERENCES section for introductory material.)  Rather, it is intended to

be reliable, portable, industrial-strength code.  We do not claim to have

achieved that goal in every aspect of the software, but we strive for it.

We welcome the use of this software as a component of commercial products.

No royalty is required, but we do ask for an acknowledgement in product

documentation, as described under LEGAL ISSUES.

LEGAL ISSUES

============

In plain English:

1. We don't promise that this software works.  (But if you find any bugs,

   please let us know!)

2. You can use this software for whatever you want.  You don't have to pay us.

3. You may not pretend that you wrote this software.  If you use it in a

   program, you must acknowledge somewhere in your documentation that

   you've used the IJG code.

In legalese:

The authors make NO WARRANTY or representation, either express or implied,

with respect to this software, its quality, accuracy, merchantability, or

fitness for a particular purpose.  This software is provided "AS IS", and you,

its user, assume the entire risk as to its quality and accuracy.

This software is copyright (C) 1991-2013, Thomas G. Lane, Guido Vollbeding.

All Rights Reserved except as specified below.

Permission is hereby granted to use, copy, modify, and distribute this

software (or portions thereof) for any purpose, without fee, subject to these

conditions:

(1) If any part of the source code for this software is distributed, then this

README file must be included, with this copyright and no-warranty notice

unaltered; and any additions, deletions, or changes to the original files

must be clearly indicated in accompanying documentation.

(2) If only executable code is distributed, then the accompanying

documentation must state that "this software is based in part on the work of

the Independent JPEG Group".

(3) Permission for use of this software is granted only if the user accepts

full responsibility for any undesirable consequences; the authors accept

NO LIABILITY for damages of any kind.

These conditions apply to any software derived from or based on the IJG code,

not just to the unmodified library.  If you use our work, you ought to

acknowledge us.

Permission is NOT granted for the use of any IJG author's name or company name

in advertising or publicity relating to this software or products derived from

it.  This software may be referred to only as "the Independent JPEG Group's

software".

We specifically permit and encourage the use of this software as the basis of

commercial products, provided that all warranty or liability claims are

assumed by the product vendor.

The Unix configuration script "configure" was produced with GNU Autoconf.

It is copyright by the Free Software Foundation but is freely distributable.

The same holds for its supporting scripts (config.guess, config.sub,

ltmain.sh).  Another support script, install-sh, is copyright by X Consortium

but is also freely distributable.

The IJG distribution formerly included code to read and write GIF files.

To avoid entanglement with the Unisys LZW patent, GIF reading support has

been removed altogether, and the GIF writer has been simplified to produce

"uncompressed GIFs".  This technique does not use the LZW algorithm; the

resulting GIF files are larger than usual, but are readable by all standard

GIF decoders.

We are required to state that

    "The Graphics Interchange Format(c) is the Copyright property of

    CompuServe Incorporated.  GIF(sm) is a Service Mark property of

    CompuServe Incorporated."

REFERENCES

==========

We recommend reading one or more of these references before trying to

understand the innards of the JPEG software.

The best short technical introduction to the JPEG compression algorithm is

	Wallace, Gregory K.  "The JPEG Still Picture Compression Standard",

	Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.

(Adjacent articles in that issue discuss MPEG motion picture compression,

applications of JPEG, and related topics.)  If you don't have the CACM issue

handy, a PostScript file containing a revised version of Wallace's article is

available at http://www.ijg.org/files/wallace.ps.gz.  The file (actually

a preprint for an article that appeared in IEEE Trans. Consumer Electronics)

omits the sample images that appeared in CACM, but it includes corrections

and some added material.  Note: the Wallace article is copyright ACM and IEEE,

and it may not be used for commercial purposes.

A somewhat less technical, more leisurely introduction to JPEG can be found in

"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by

M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1.  This book provides

good explanations and example C code for a multitude of compression methods

including JPEG.  It is an excellent source if you are comfortable reading C

code but don't know much about data compression in general.  The book's JPEG

sample code is far from industrial-strength, but when you are ready to look

at a full implementation, you've got one here...

The best currently available description of JPEG is the textbook "JPEG Still

Image Data Compression Standard" by William B. Pennebaker and Joan L.

Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.

Price US$59.95, 638 pp.  The book includes the complete text of the ISO JPEG

standards (DIS 10918-1 and draft DIS 10918-2).

Although this is by far the most detailed and comprehensive exposition of

JPEG publicly available, we point out that it is still missing an explanation

of the most essential properties and algorithms of the underlying DCT

technology.

If you think that you know about DCT-based JPEG after reading this book,

then you are in delusion.  The real fundamentals and corresponding potential

of DCT-based JPEG are not publicly known so far, and that is the reason for

all the mistaken developments taking place in the image coding domain.

The original JPEG standard is divided into two parts, Part 1 being the actual

specification, while Part 2 covers compliance testing methods.  Part 1 is

titled "Digital Compression and Coding of Continuous-tone Still Images,

Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS

10918-1, ITU-T T.81.  Part 2 is titled "Digital Compression and Coding of

Continuous-tone Still Images, Part 2: Compliance testing" and has document

numbers ISO/IEC IS 10918-2, ITU-T T.83.

IJG JPEG 8 introduced an implementation of the JPEG SmartScale extension

which is specified in two documents:  A contributed document at ITU and ISO

with title "ITU-T JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced

Image Coding", April 2006, Geneva, Switzerland.  The latest version of this

document is Revision 3.  And a contributed document ISO/IEC JTC1/SC29/WG1 N

5799 with title "Evolution of JPEG", June/July 2011, Berlin, Germany.

IJG JPEG 9 introduces a reversible color transform for improved lossless

compression which is described in a contributed document ISO/IEC JTC1/SC29/

WG1 N 6080 with title "JPEG 9 Lossless Coding", June/July 2012, Paris,

France.

The JPEG standard does not specify all details of an interchangeable file

format.  For the omitted details we follow the "JFIF" conventions, revision

1.02.  JFIF 1.02 has been adopted as an Ecma International Technical Report

and thus received a formal publication status.  It is available as a free

download in PDF format from

http://www.ecma-international.org/publications/techreports/E-TR-098.htm.

A PostScript version of the JFIF document is available at

http://www.ijg.org/files/jfif.ps.gz.  There is also a plain text version at

http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures.

The TIFF 6.0 file format specification can be obtained by FTP from

ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz.  The JPEG incorporation scheme

found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.

IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).

Instead, we recommend the JPEG design proposed by TIFF Technical Note #2

(Compression tag 7).  Copies of this Note can be obtained from

http://www.ijg.org/files/.  It is expected that the next revision

of the TIFF spec will replace the 6.0 JPEG design with the Note's design.

Although IJG's own code does not support TIFF/JPEG, the free libtiff library

uses our library to implement TIFF/JPEG per the Note.

ARCHIVE LOCATIONS

=================

The "official" archive site for this software is www.ijg.org.

The most recent released version can always be found there in

directory "files".  This particular version will be archived as

http://www.ijg.org/files/jpegsrc.v9.tar.gz, and in Windows-compatible

"zip" archive format as http://www.ijg.org/files/jpegsr9.zip.

The JPEG FAQ (Frequently Asked Questions) article is a source of some

general information about JPEG.

It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/

and other news.answers archive sites, including the official news.answers

archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.

If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu

with body

	send usenet/news.answers/jpeg-faq/part1

	send usenet/news.answers/jpeg-faq/part2

ACKNOWLEDGMENTS

===============

Thank to Juergen Bruder for providing me with a copy of the common DCT

algorithm article, only to find out that I had come to the same result

in a more direct and comprehensible way with a more generative approach.

Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the

ITU JPEG (Study Group 16) meeting in Geneva, Switzerland.

Thank to Thomas Wiegand and Gary Sullivan for inviting me to the

Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland.

Thank to Thomas Richter and Daniel Lee for inviting me to the

ISO/IEC JTC1/SC29/WG1 (also known as JPEG, together with ITU-T SG16)

meeting in Berlin, Germany.

Thank to John Korejwa and Massimo Ballerini for inviting me to

fruitful consultations in Boston, MA and Milan, Italy.

Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther

Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel

for corresponding business development.

Thank to Nico Zschach and Dirk Stelling of the technical support team

at the Digital Images company in Halle for providing me with extra

equipment for configuration tests.

Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful

communication about JPEG configuration in Sigma Photo Pro software.

Thank to Andrew Finkenstadt for hosting the ijg.org site.

Last but not least special thank to Thomas G. Lane for the original

design and development of this singular software package.

FILE FORMAT WARS

================

The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together

with ITU-T SG16) currently promotes different formats containing the name

"JPEG" which is misleading because these formats are incompatible with

original DCT-based JPEG and are based on faulty technologies.

IJG therefore does not and will not support such momentary mistakes

(see REFERENCES).

There exist also distributions under the name "OpenJPEG" promoting such

kind of formats which is misleading because they don't support original

JPEG images.

We have no sympathy for the promotion of inferior formats.  Indeed, one of

the original reasons for developing this free software was to help force

convergence on common, interoperable format standards for JPEG files.

Don't use an incompatible file format!

(In any case, our decoder will remain capable of reading existing JPEG

image files indefinitely.)

Furthermore, the ISO committee pretends to be "responsible for the popular

JPEG" in their public reports which is not true because they don't respond to

actual requirements for the maintenance of the original JPEG specification.

There are currently different distributions in circulation containing the

name "libjpeg" which is misleading because they don't have the features and

are incompatible with formats supported by actual IJG libjpeg distributions.

One of those fakes is released by members of the ISO committee and just uses

the name of libjpeg for misdirection of people, similar to the abuse of the

name JPEG as described above, while having nothing in common with actual IJG

libjpeg distributions.

The other one claims to be a "derivative" or "fork" of the original libjpeg

and violates the license conditions as described under LEGAL ISSUES above.

We have no sympathy for the release of misleading and illegal distributions

derived from obsolete code bases.

Don't use an obsolete code base!

TO DO

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Version 9 is the second release of a new generation JPEG standard

to overcome the limitations of the original JPEG specification.

More features are being prepared for coming releases...

Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.