1 The Independent JPEG Group's JPEG software
   2 ==========================================
   3 
   4 README for release 9c of 14-Jan-2018
   5 ====================================
   6 
   7 This distribution contains the ninth public release of the Independent JPEG
   8 Group's free JPEG software.  You are welcome to redistribute this software and
   9 to use it for any purpose, subject to the conditions under LEGAL ISSUES, below.
  10 
  11 This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone,
  12 Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson,
  13 Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers,
  14 and other members of the Independent JPEG Group.
  15 
  16 IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee
  17 (previously known as JPEG, together with ITU-T SG16).
  18 
  19 
  20 DOCUMENTATION ROADMAP
  21 =====================
  22 
  23 This file contains the following sections:
  24 
  25 OVERVIEW            General description of JPEG and the IJG software.
  26 LEGAL ISSUES        Copyright, lack of warranty, terms of distribution.
  27 REFERENCES          Where to learn more about JPEG.
  28 ARCHIVE LOCATIONS   Where to find newer versions of this software.
  29 ACKNOWLEDGMENTS     Special thanks.
  30 FILE FORMAT WARS    Software *not* to get.
  31 TO DO               Plans for future IJG releases.
  32 
  33 Other documentation files in the distribution are:
  34 
  35 User 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.
  42 Programmer 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 
  49 Please read at least the files install.txt and usage.txt.  Some information
  50 can also be found in the JPEG FAQ (Frequently Asked Questions) article.  See
  51 ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.
  52 
  53 If you want to understand how the JPEG code works, we suggest reading one or
  54 more of the REFERENCES, then looking at the documentation files (in roughly
  55 the order listed) before diving into the code.
  56 
  57 
  58 OVERVIEW
  59 ========
  60 
  61 This package contains C software to implement JPEG image encoding, decoding,
  62 and transcoding.  JPEG (pronounced "jay-peg") is a standardized compression
  63 method for full-color and grayscale images.
  64 
  65 This software implements JPEG baseline, extended-sequential, and progressive
  66 compression processes.  Provision is made for supporting all variants of these
  67 processes, although some uncommon parameter settings aren't implemented yet.
  68 We have made no provision for supporting the hierarchical or lossless
  69 processes defined in the standard.
  70 
  71 We provide a set of library routines for reading and writing JPEG image files,
  72 plus two sample applications "cjpeg" and "djpeg", which use the library to
  73 perform conversion between JPEG and some other popular image file formats.
  74 The library is intended to be reused in other applications.
  75 
  76 In order to support file conversion and viewing software, we have included
  77 considerable functionality beyond the bare JPEG coding/decoding capability;
  78 for example, the color quantization modules are not strictly part of JPEG
  79 decoding, but they are essential for output to colormapped file formats or
  80 colormapped displays.  These extra functions can be compiled out of the
  81 library if not required for a particular application.
  82 
  83 We have also included "jpegtran", a utility for lossless transcoding between
  84 different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple
  85 applications for inserting and extracting textual comments in JFIF files.
  86 
  87 The emphasis in designing this software has been on achieving portability and
  88 flexibility, while also making it fast enough to be useful.  In particular,
  89 the software is not intended to be read as a tutorial on JPEG.  (See the
  90 REFERENCES section for introductory material.)  Rather, it is intended to
  91 be reliable, portable, industrial-strength code.  We do not claim to have
  92 achieved that goal in every aspect of the software, but we strive for it.
  93 
  94 We welcome the use of this software as a component of commercial products.
  95 No royalty is required, but we do ask for an acknowledgement in product
  96 documentation, as described under LEGAL ISSUES.
  97 
  98 
  99 LEGAL ISSUES
 100 ============
 101 
 102 In plain English:
 103 
 104 1. We don't promise that this software works.  (But if you find any bugs,
 105    please let us know!)
 106 2. You can use this software for whatever you want.  You don't have to pay us.
 107 3. 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 
 111 In legalese:
 112 
 113 The authors make NO WARRANTY or representation, either express or implied,
 114 with respect to this software, its quality, accuracy, merchantability, or
 115 fitness for a particular purpose.  This software is provided "AS IS", and you,
 116 its user, assume the entire risk as to its quality and accuracy.
 117 
 118 This software is copyright (C) 1991-2018, Thomas G. Lane, Guido Vollbeding.
 119 All Rights Reserved except as specified below.
 120 
 121 Permission is hereby granted to use, copy, modify, and distribute this
 122 software (or portions thereof) for any purpose, without fee, subject to these
 123 conditions:
 124 (1) If any part of the source code for this software is distributed, then this
 125 README file must be included, with this copyright and no-warranty notice
 126 unaltered; and any additions, deletions, or changes to the original files
 127 must be clearly indicated in accompanying documentation.
 128 (2) If only executable code is distributed, then the accompanying
 129 documentation must state that "this software is based in part on the work of
 130 the Independent JPEG Group".
 131 (3) Permission for use of this software is granted only if the user accepts
 132 full responsibility for any undesirable consequences; the authors accept
 133 NO LIABILITY for damages of any kind.
 134 
 135 These conditions apply to any software derived from or based on the IJG code,
 136 not just to the unmodified library.  If you use our work, you ought to
 137 acknowledge us.
 138 
 139 Permission is NOT granted for the use of any IJG author's name or company name
 140 in advertising or publicity relating to this software or products derived from
 141 it.  This software may be referred to only as "the Independent JPEG Group's
 142 software".
 143 
 144 We specifically permit and encourage the use of this software as the basis of
 145 commercial products, provided that all warranty or liability claims are
 146 assumed by the product vendor.
 147 
 148 
 149 The Unix configuration script "configure" was produced with GNU Autoconf.
 150 It is copyright by the Free Software Foundation but is freely distributable.
 151 The same holds for its supporting scripts (config.guess, config.sub,
 152 ltmain.sh).  Another support script, install-sh, is copyright by X Consortium
 153 but is also freely distributable.
 154 
 155 The IJG distribution formerly included code to read and write GIF files.
 156 To avoid entanglement with the Unisys LZW patent (now expired), GIF reading
 157 support has been removed altogether, and the GIF writer has been simplified
 158 to produce "uncompressed GIFs".  This technique does not use the LZW
 159 algorithm; the resulting GIF files are larger than usual, but are readable
 160 by all standard GIF decoders.
 161 
 162 
 163 REFERENCES
 164 ==========
 165 
 166 We recommend reading one or more of these references before trying to
 167 understand the innards of the JPEG software.
 168 
 169 The best short technical introduction to the JPEG compression algorithm is
 170         Wallace, Gregory K.  "The JPEG Still Picture Compression Standard",
 171         Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
 172 (Adjacent articles in that issue discuss MPEG motion picture compression,
 173 applications of JPEG, and related topics.)  If you don't have the CACM issue
 174 handy, a PDF file containing a revised version of Wallace's article is
 175 available at http://www.ijg.org/files/Wallace.JPEG.pdf.  The file (actually
 176 a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
 177 omits the sample images that appeared in CACM, but it includes corrections
 178 and some added material.  Note: the Wallace article is copyright ACM and IEEE,
 179 and it may not be used for commercial purposes.
 180 
 181 A somewhat less technical, more leisurely introduction to JPEG can be found in
 182 "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by
 183 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1.  This book provides
 184 good explanations and example C code for a multitude of compression methods
 185 including JPEG.  It is an excellent source if you are comfortable reading C
 186 code but don't know much about data compression in general.  The book's JPEG
 187 sample code is far from industrial-strength, but when you are ready to look
 188 at a full implementation, you've got one here...
 189 
 190 The best currently available description of JPEG is the textbook "JPEG Still
 191 Image Data Compression Standard" by William B. Pennebaker and Joan L.
 192 Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
 193 Price US$59.95, 638 pp.  The book includes the complete text of the ISO JPEG
 194 standards (DIS 10918-1 and draft DIS 10918-2).
 195 Although this is by far the most detailed and comprehensive exposition of
 196 JPEG publicly available, we point out that it is still missing an explanation
 197 of the most essential properties and algorithms of the underlying DCT
 198 technology.
 199 If you think that you know about DCT-based JPEG after reading this book,
 200 then you are in delusion.  The real fundamentals and corresponding potential
 201 of DCT-based JPEG are not publicly known so far, and that is the reason for
 202 all the mistaken developments taking place in the image coding domain.
 203 
 204 The original JPEG standard is divided into two parts, Part 1 being the actual
 205 specification, while Part 2 covers compliance testing methods.  Part 1 is
 206 titled "Digital Compression and Coding of Continuous-tone Still Images,
 207 Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
 208 10918-1, ITU-T T.81.  Part 2 is titled "Digital Compression and Coding of
 209 Continuous-tone Still Images, Part 2: Compliance testing" and has document
 210 numbers ISO/IEC IS 10918-2, ITU-T T.83.
 211 IJG JPEG 8 introduced an implementation of the JPEG SmartScale extension
 212 which is specified in two documents:  A contributed document at ITU and ISO
 213 with title "ITU-T JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced
 214 Image Coding", April 2006, Geneva, Switzerland.  The latest version of this
 215 document is Revision 3.  And a contributed document ISO/IEC JTC1/SC29/WG1 N
 216 5799 with title "Evolution of JPEG", June/July 2011, Berlin, Germany.
 217 IJG JPEG 9 introduces a reversible color transform for improved lossless
 218 compression which is described in a contributed document ISO/IEC JTC1/SC29/
 219 WG1 N 6080 with title "JPEG 9 Lossless Coding", June/July 2012, Paris,
 220 France.
 221 
 222 The JPEG standard does not specify all details of an interchangeable file
 223 format.  For the omitted details we follow the "JFIF" conventions, version 2.
 224 JFIF version 1 has been adopted as Recommendation ITU-T T.871 (05/2011) :
 225 Information technology - Digital compression and coding of continuous-tone
 226 still images: JPEG File Interchange Format (JFIF).  It is available as a
 227 free download in PDF file format from http://www.itu.int/rec/T-REC-T.871.
 228 A PDF file of the older JFIF document is available at
 229 http://www.w3.org/Graphics/JPEG/jfif3.pdf.
 230 
 231 The TIFF 6.0 file format specification can be obtained by FTP from
 232 ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz.  The JPEG incorporation scheme
 233 found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.
 234 IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).
 235 Instead, we recommend the JPEG design proposed by TIFF Technical Note #2
 236 (Compression tag 7).  Copies of this Note can be obtained from
 237 http://www.ijg.org/files/.  It is expected that the next revision
 238 of the TIFF spec will replace the 6.0 JPEG design with the Note's design.
 239 Although IJG's own code does not support TIFF/JPEG, the free libtiff library
 240 uses our library to implement TIFF/JPEG per the Note.
 241 
 242 
 243 ARCHIVE LOCATIONS
 244 =================
 245 
 246 The "official" archive site for this software is www.ijg.org.
 247 The most recent released version can always be found there in
 248 directory "files".  This particular version will be archived as
 249 http://www.ijg.org/files/jpegsrc.v9c.tar.gz, and in Windows-compatible
 250 "zip" archive format as http://www.ijg.org/files/jpegsr9c.zip.
 251 
 252 The JPEG FAQ (Frequently Asked Questions) article is a source of some
 253 general information about JPEG.
 254 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/
 255 and other news.answers archive sites, including the official news.answers
 256 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.
 257 If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu
 258 with body
 259         send usenet/news.answers/jpeg-faq/part1
 260         send usenet/news.answers/jpeg-faq/part2
 261 
 262 
 263 ACKNOWLEDGMENTS
 264 ===============
 265 
 266 Thank to Juergen Bruder for providing me with a copy of the common DCT
 267 algorithm article, only to find out that I had come to the same result
 268 in a more direct and comprehensible way with a more generative approach.
 269 
 270 Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the
 271 ITU JPEG (Study Group 16) meeting in Geneva, Switzerland.
 272 
 273 Thank to Thomas Wiegand and Gary Sullivan for inviting me to the
 274 Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland.
 275 
 276 Thank to Thomas Richter and Daniel Lee for inviting me to the
 277 ISO/IEC JTC1/SC29/WG1 (previously known as JPEG, together with ITU-T SG16)
 278 meeting in Berlin, Germany.
 279 
 280 Thank to John Korejwa and Massimo Ballerini for inviting me to
 281 fruitful consultations in Boston, MA and Milan, Italy.
 282 
 283 Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther
 284 Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel
 285 for corresponding business development.
 286 
 287 Thank to Nico Zschach and Dirk Stelling of the technical support team
 288 at the Digital Images company in Halle for providing me with extra
 289 equipment for configuration tests.
 290 
 291 Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful
 292 communication about JPEG configuration in Sigma Photo Pro software.
 293 
 294 Thank to Andrew Finkenstadt for hosting the ijg.org site.
 295 
 296 Thank to Thomas G. Lane for the original design and development of
 297 this singular software package.
 298 
 299 Thank to Lars Goehler, Andreas Heinecke, Sebastian Fuss, Yvonne Roebert,
 300 Andrej Werner, and Ulf-Dietrich Braumann for support and public relations.
 301 
 302 
 303 FILE FORMAT WARS
 304 ================
 305 
 306 The ISO/IEC JTC1/SC29/WG1 standards committee (previously known as JPEG,
 307 together with ITU-T SG16) currently promotes different formats containing
 308 the name "JPEG" which is misleading because these formats are incompatible
 309 with original DCT-based JPEG and are based on faulty technologies.
 310 IJG therefore does not and will not support such momentary mistakes
 311 (see REFERENCES).
 312 There exist also distributions under the name "OpenJPEG" promoting such
 313 kind of formats which is misleading because they don't support original
 314 JPEG images.
 315 We have no sympathy for the promotion of inferior formats.  Indeed, one of
 316 the original reasons for developing this free software was to help force
 317 convergence on common, interoperable format standards for JPEG files.
 318 Don't use an incompatible file format!
 319 (In any case, our decoder will remain capable of reading existing JPEG
 320 image files indefinitely.)
 321 
 322 The ISO committee pretends to be "responsible for the popular JPEG" in their
 323 public reports which is not true because they don't respond to actual
 324 requirements for the maintenance of the original JPEG specification.
 325 Furthermore, the ISO committee pretends to "ensure interoperability" with
 326 their standards which is not true because their "standards" support only
 327 application-specific and proprietary use cases and contain mathematically
 328 incorrect code.
 329 
 330 There are currently different distributions in circulation containing the
 331 name "libjpeg" which is misleading because they don't have the features and
 332 are incompatible with formats supported by actual IJG libjpeg distributions.
 333 One of those fakes is released by members of the ISO committee and just uses
 334 the name of libjpeg for misdirection of people, similar to the abuse of the
 335 name JPEG as described above, while having nothing in common with actual IJG
 336 libjpeg distributions and containing mathematically incorrect code.
 337 The other one claims to be a "derivative" or "fork" of the original libjpeg,
 338 but violates the license conditions as described under LEGAL ISSUES above
 339 and violates basic C programming properties.
 340 We have no sympathy for the release of misleading, incorrect and illegal
 341 distributions derived from obsolete code bases.
 342 Don't use an obsolete code base!
 343 
 344 According to the UCC (Uniform Commercial Code) law, IJG has the lawful and
 345 legal right to foreclose on certain standardization bodies and other
 346 institutions or corporations that knowingly perform substantial and
 347 systematic deceptive acts and practices, fraud, theft, and damaging of the
 348 value of the people of this planet without their knowing, willing and
 349 intentional consent.
 350 The titles, ownership, and rights of these institutions and all their assets
 351 are now duly secured and held in trust for the free people of this planet.
 352 People of the planet, on every country, may have a financial interest in
 353 the assets of these former principals, agents, and beneficiaries of the
 354 foreclosed institutions and corporations.
 355 IJG asserts what is: that each man, woman, and child has unalienable value
 356 and rights granted and deposited in them by the Creator and not any one of
 357 the people is subordinate to any artificial principality, corporate fiction
 358 or the special interest of another without their appropriate knowing,
 359 willing and intentional consent made by contract or accommodation agreement.
 360 IJG expresses that which already was.
 361 The people have already determined and demanded that public administration
 362 entities, national governments, and their supporting judicial systems must
 363 be fully transparent, accountable, and liable.
 364 IJG has secured the value for all concerned free people of the planet.
 365 
 366 A partial list of foreclosed institutions and corporations ("Hall of Shame")
 367 is currently prepared and will be published later.
 368 
 369 
 370 TO DO
 371 =====
 372 
 373 Version 9 is the second release of a new generation JPEG standard
 374 to overcome the limitations of the original JPEG specification,
 375 and is the first true source reference JPEG codec.
 376 More features are being prepared for coming releases...
 377 
 378 Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.