README - third_party/libjpeg-turbo - Git at Google

 libjpeg-turbo note:  This file has been modified by The libjpeg-turbo Project
 to include only information relevant to libjpeg-turbo, to wordsmith certain
 sections, and to remove impolitic language that existed in the libjpeg v8
 README.  It is included only for reference.  Please see README-turbo.txt for
 information specific to libjpeg-turbo.


 The Independent JPEG Group's JPEG software
 ==========================================

 This distribution contains a 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.
 FILE FORMAT WARS    Software *not* to get.
 TO DO               Plans for future IJG releases.

 Other documentation files in the distribution are:

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

 Please read at least 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 grayscale images.  JPEG's strong suit is compressing
 photographic images or other types of images that have smooth color and
 brightness transitions between neighboring pixels.  Images with sharp lines or
 other abrupt features may not compress well with JPEG, and a higher JPEG
 quality may have to be used to avoid visible compression artifacts with such
 images.

 JPEG is lossy, meaning that the output pixels are not necessarily identical to
 the input pixels.  However, on photographic content and other "smooth" images,
 very good compression ratios can be obtained with no visible compression
 artifacts, and extremely high compression ratios are possible if you are
 willing to sacrifice image quality (by reducing the "quality" setting in the
 compressor.)

 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) 1991-2012, 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).

 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.

 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.v8d.tar.gz, and in Windows-compatible
 "zip" archive format as http://www.ijg.org/files/jpegsr8d.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


 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 are incompatible with original DCT-based JPEG.  IJG therefore does
 not support these formats (see REFERENCES).  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.)


 TO DO
 =====

 Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.
	libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project
	to include only information relevant to libjpeg-turbo, to wordsmith certain
	sections, and to remove impolitic language that existed in the libjpeg v8
	README. It is included only for reference. Please see README-turbo.txt for
	information specific to libjpeg-turbo.


	The Independent JPEG Group's JPEG software
	==========================================

	This distribution contains a 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.
	FILE FORMAT WARS Software not to get.
	TO DO Plans for future IJG releases.

	Other documentation files in the distribution are:

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

	Please read at least 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 grayscale images. JPEG's strong suit is compressing
	photographic images or other types of images that have smooth color and
	brightness transitions between neighboring pixels. Images with sharp lines or
	other abrupt features may not compress well with JPEG, and a higher JPEG
	quality may have to be used to avoid visible compression artifacts with such
	images.

	JPEG is lossy, meaning that the output pixels are not necessarily identical to
	the input pixels. However, on photographic content and other "smooth" images,
	very good compression ratios can be obtained with no visible compression
	artifacts, and extremely high compression ratios are possible if you are
	willing to sacrifice image quality (by reducing the "quality" setting in the
	compressor.)

	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) 1991-2012, 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).

	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.

	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.v8d.tar.gz, and in Windows-compatible
	"zip" archive format as http://www.ijg.org/files/jpegsr8d.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


	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 are incompatible with original DCT-based JPEG. IJG therefore does
	not support these formats (see REFERENCES). 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.)


	TO DO
	=====

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