Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 1 | The Independent JPEG Group's JPEG software |
| 2 | ========================================== |
| 3 | |
Thomas G. Lane | 9ba2f5e | 1994-12-07 00:00:00 +0000 | [diff] [blame^] | 4 | README for release 5a of 7-Dec-94 |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 5 | ================================= |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 6 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 7 | This distribution contains the fifth public release of the Independent JPEG |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 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 | |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 11 | Serious users of this software (particularly those incorporating it into |
Thomas G. Lane | 9ba2f5e | 1994-12-07 00:00:00 +0000 | [diff] [blame^] | 12 | larger programs) should contact IJG at jpeg-info@uunet.uu.net to be added to |
| 13 | our electronic mailing list. Mailing list members are notified of updates |
| 14 | and have a chance to participate in technical discussions, etc. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 15 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 16 | This software is the work of Tom Lane, Philip Gladstone, Luis Ortiz, Jim |
| 17 | Boucher, Lee Crocker, George Phillips, Davide Rossi, Ge' Weijers, and other |
| 18 | members of the Independent JPEG Group. |
| 19 | |
| 20 | IJG is not associated with the official ISO JPEG standards committee. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 21 | |
| 22 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 23 | DOCUMENTATION ROADMAP |
| 24 | ===================== |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 25 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 26 | This file contains the following sections: |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 27 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 28 | OVERVIEW General description of JPEG and the IJG software. |
| 29 | LEGAL ISSUES Copyright, lack of warranty, terms of distribution. |
| 30 | REFERENCES Where to learn more about JPEG. |
| 31 | ARCHIVE LOCATIONS Where to find newer versions of this software. |
| 32 | RELATED SOFTWARE Other stuff you should get. |
| 33 | FILE FORMAT WARS Software *not* to get. |
| 34 | TO DO Plans for future IJG releases. |
| 35 | |
| 36 | Other documentation files in the distribution are: |
| 37 | |
| 38 | User documentation: |
| 39 | install.doc How to configure and install the IJG software. |
| 40 | usage.doc Usage instructions for cjpeg, djpeg, rdjpgcom, wrjpgcom. |
| 41 | *.1 Unix-style man pages for programs (same info as usage.doc). |
| 42 | change.log Version-to-version change highlights. |
| 43 | Programmer and internal documentation: |
| 44 | libjpeg.doc How to use the JPEG library in your own programs. |
| 45 | example.c Sample code for calling the JPEG library. |
| 46 | structure.doc Overview of the JPEG library's internal structure. |
| 47 | filelist.doc Road map of IJG files. |
| 48 | coderules.doc Coding style rules --- please read if you contribute code. |
| 49 | |
| 50 | Please read at least the files install.doc and usage.doc. Useful information |
| 51 | can also be found in the JPEG FAQ (Frequently Asked Questions) article. See |
| 52 | ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. |
| 53 | |
| 54 | If you want to understand how the JPEG code works, we suggest reading one or |
| 55 | more of the REFERENCES, then looking at the documentation files (in roughly |
| 56 | the order listed) before diving into the code. |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 57 | |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 58 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 59 | OVERVIEW |
| 60 | ======== |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 61 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 62 | This package contains C software to implement JPEG image compression and |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 63 | decompression. JPEG (pronounced "jay-peg") is a standardized compression |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 64 | method for full-color and gray-scale images. JPEG is intended for compressing |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 65 | "real-world" scenes; cartoons and other non-realistic images are not its |
| 66 | strong suit. JPEG is lossy, meaning that the output image is not necessarily |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 67 | identical to the input image. Hence you must not use JPEG if you have to have |
| 68 | identical output bits. However, on typical images of real-world scenes, very |
| 69 | good compression levels can be obtained with no visible change, and amazingly |
| 70 | high compression levels are possible if you can tolerate a low-quality image. |
| 71 | For more details, see the references, or just experiment with various |
| 72 | compression settings. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 73 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 74 | We provide a set of library routines for reading and writing JPEG image files, |
| 75 | plus two simple applications "cjpeg" and "djpeg", which use the library to |
| 76 | perform conversion between JPEG and some other popular image file formats. |
| 77 | The library is intended to be reused in other applications. |
| 78 | |
| 79 | This software implements JPEG baseline and extended-sequential compression |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 80 | processes. Provision is made for supporting all variants of these processes, |
| 81 | although some uncommon parameter settings aren't implemented yet. For legal |
| 82 | reasons, we are not distributing code for the arithmetic-coding process; see |
| 83 | LEGAL ISSUES. At present we have made no provision for supporting the |
Thomas G. Lane | 4a6b730 | 1992-03-17 00:00:00 +0000 | [diff] [blame] | 84 | progressive, hierarchical, or lossless processes defined in the standard. |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 85 | (Support for progressive mode may be offered in a future release.) |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 86 | |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 87 | In order to support file conversion and viewing software, we have included |
| 88 | considerable functionality beyond the bare JPEG coding/decoding capability; |
| 89 | for example, the color quantization modules are not strictly part of JPEG |
| 90 | decoding, but they are essential for output to colormapped file formats or |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 91 | colormapped displays. These extra functions can be compiled out of the |
| 92 | library if not required for a particular application. We have also included |
| 93 | two simple applications for inserting and extracting textual comments in |
| 94 | JFIF files. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 95 | |
| 96 | The emphasis in designing this software has been on achieving portability and |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 97 | flexibility, while also making it fast enough to be useful. In particular, |
| 98 | the software is not intended to be read as a tutorial on JPEG. (See the |
| 99 | REFERENCES section for introductory material.) While we hope that the entire |
| 100 | package will someday be industrial-strength code, much remains to be done in |
| 101 | performance tuning and in improving the capabilities of individual modules. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 102 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 103 | We welcome the use of this software as a component of commercial products. |
| 104 | No royalty is required, but we do ask for an acknowledgement in product |
| 105 | documentation, as described under LEGAL ISSUES. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 106 | |
| 107 | |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 108 | LEGAL ISSUES |
| 109 | ============ |
| 110 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 111 | In plain English: |
| 112 | |
| 113 | 1. We don't promise that this software works. (But if you find any bugs, |
| 114 | please let us know!) |
| 115 | 2. You can use this software for whatever you want. You don't have to pay us. |
| 116 | 3. You may not pretend that you wrote this software. If you use it in a |
| 117 | program, you must acknowledge somewhere in your documentation that |
| 118 | you've used the IJG code. |
| 119 | |
| 120 | In legalese: |
| 121 | |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 122 | The authors make NO WARRANTY or representation, either express or implied, |
| 123 | with respect to this software, its quality, accuracy, merchantability, or |
| 124 | fitness for a particular purpose. This software is provided "AS IS", and you, |
| 125 | its user, assume the entire risk as to its quality and accuracy. |
| 126 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 127 | This software is copyright (C) 1991, 1992, 1993, 1994, Thomas G. Lane. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 128 | All Rights Reserved except as specified below. |
| 129 | |
| 130 | Permission is hereby granted to use, copy, modify, and distribute this |
| 131 | software (or portions thereof) for any purpose, without fee, subject to these |
| 132 | conditions: |
| 133 | (1) If any part of the source code for this software is distributed, then this |
| 134 | README file must be included, with this copyright and no-warranty notice |
| 135 | unaltered; and any additions, deletions, or changes to the original files |
| 136 | must be clearly indicated in accompanying documentation. |
| 137 | (2) If only executable code is distributed, then the accompanying |
| 138 | documentation must state that "this software is based in part on the work of |
| 139 | the Independent JPEG Group". |
| 140 | (3) Permission for use of this software is granted only if the user accepts |
| 141 | full responsibility for any undesirable consequences; the authors accept |
| 142 | NO LIABILITY for damages of any kind. |
| 143 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 144 | These conditions apply to any software derived from or based on the IJG code, |
| 145 | not just to the unmodified library. If you use our work, you ought to |
| 146 | acknowledge us. |
| 147 | |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 148 | Permission is NOT granted for the use of any IJG author's name or company name |
| 149 | in advertising or publicity relating to this software or products derived from |
| 150 | it. This software may be referred to only as "the Independent JPEG Group's |
| 151 | software". |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 152 | |
| 153 | We specifically permit and encourage the use of this software as the basis of |
| 154 | commercial products, provided that all warranty or liability claims are |
| 155 | assumed by the product vendor. |
| 156 | |
| 157 | |
| 158 | ansi2knr.c is included in this distribution by permission of L. Peter Deutsch, |
| 159 | sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA. |
| 160 | ansi2knr.c is NOT covered by the above copyright and conditions, but instead |
| 161 | by the usual distribution terms of the Free Software Foundation; principally, |
| 162 | that you must include source code if you redistribute it. (See the file |
| 163 | ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 164 | of any program generated from the IJG code, this does not limit you more than |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 165 | the foregoing paragraphs do. |
| 166 | |
Thomas G. Lane | 9ba2f5e | 1994-12-07 00:00:00 +0000 | [diff] [blame^] | 167 | The configuration script "configure" was produced with GNU Autoconf. It |
| 168 | is copyright by the Free Software Foundation but is freely distributable. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 169 | |
| 170 | It appears that the arithmetic coding option of the JPEG spec is covered by |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 171 | patents owned by IBM, AT&T, and Mitsubishi. Hence arithmetic coding cannot |
| 172 | legally be used without obtaining one or more licenses. For this reason, |
| 173 | support for arithmetic coding has been removed from the free JPEG software. |
| 174 | (Since arithmetic coding provides only a marginal gain over the unpatented |
| 175 | Huffman mode, it is unlikely that very many implementations will support it.) |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 176 | So far as we are aware, there are no patent restrictions on the remaining |
| 177 | code. |
| 178 | |
Thomas G. Lane | bd543f0 | 1991-12-13 00:00:00 +0000 | [diff] [blame] | 179 | We are required to state that |
| 180 | "The Graphics Interchange Format(c) is the Copyright property of |
| 181 | CompuServe Incorporated. GIF(sm) is a Service Mark property of |
| 182 | CompuServe Incorporated." |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 183 | |
| 184 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 185 | REFERENCES |
| 186 | ========== |
| 187 | |
| 188 | We highly recommend reading one or more of these references before trying to |
| 189 | understand the innards of the JPEG software. |
| 190 | |
| 191 | The best short technical introduction to the JPEG compression algorithm is |
| 192 | Wallace, Gregory K. "The JPEG Still Picture Compression Standard", |
| 193 | Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. |
| 194 | (Adjacent articles in that issue discuss MPEG motion picture compression, |
| 195 | applications of JPEG, and related topics.) If you don't have the CACM issue |
Thomas G. Lane | 9ba2f5e | 1994-12-07 00:00:00 +0000 | [diff] [blame^] | 196 | handy, a PostScript file containing a revised version of Wallace's article |
| 197 | is available at ftp.uu.net, graphics/jpeg/wallace.ps.gz. The file (actually |
| 198 | a preprint for an article that appeared in IEEE Trans. Consumer Electronics) |
| 199 | omits the sample images that appeared in CACM, but it includes corrections |
| 200 | and some added material. Note: the Wallace article is copyright ACM and |
| 201 | IEEE, and it may not be used for commercial purposes. |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 202 | |
| 203 | A somewhat less technical, more leisurely introduction to JPEG can be found in |
| 204 | "The Data Compression Book" by Mark Nelson, published by M&T Books (Redwood |
| 205 | City, CA), 1991, ISBN 1-55851-216-0. This book provides good explanations and |
| 206 | example C code for a multitude of compression methods including JPEG. It is |
| 207 | an excellent source if you are comfortable reading C code but don't know much |
| 208 | about data compression in general. The book's JPEG sample code is far from |
| 209 | industrial-strength, but when you are ready to look at a full implementation, |
| 210 | you've got one here... |
| 211 | |
| 212 | The best full description of JPEG is the textbook "JPEG Still Image Data |
| 213 | Compression Standard" by William B. Pennebaker and Joan L. Mitchell, published |
| 214 | by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. Price US$59.95, 638 pp. |
| 215 | The book includes the complete text of the ISO JPEG standards (DIS 10918-1 |
| 216 | and draft DIS 10918-2). This is by far the most complete exposition of JPEG |
| 217 | in existence, and we highly recommend it. |
| 218 | |
| 219 | The JPEG standard itself is not available electronically; you must order a |
| 220 | paper copy through ISO. (Unless you feel a need to own a certified official |
| 221 | copy, we recommend buying the Pennebaker and Mitchell book instead; it's much |
| 222 | cheaper and includes a great deal of useful explanatory material.) In the US, |
| 223 | copies of the standard may be ordered from ANSI Sales at (212) 642-4900, or |
| 224 | from Global Engineering Documents at (800) 854-7179. (ANSI doesn't take |
| 225 | credit card orders, but Global does.) It's not cheap: as of 1992, ANSI was |
| 226 | charging $95 for Part 1 and $47 for Part 2, plus 7% shipping/handling. The |
| 227 | standard is divided into two parts, Part 1 being the actual specification, |
| 228 | while Part 2 covers compliance testing methods. Part 1 is titled "Digital |
| 229 | Compression and Coding of Continuous-tone Still Images, Part 1: Requirements |
| 230 | and guidelines" and has document number ISO/IEC IS 10918-1. As of mid-1994, |
| 231 | Part 2 is still at Draft International Standard status. It is titled "Digital |
| 232 | Compression and Coding of Continuous-tone Still Images, Part 2: Compliance |
| 233 | testing" and has document number ISO/IEC DIS 10918-2. (The document number |
| 234 | will change to IS 10918-2 when final approval is obtained.) A Part 3, |
| 235 | covering extensions, is likely to appear in draft form in late 1994. |
| 236 | |
| 237 | The JPEG standard does not specify all details of an interchangeable file |
| 238 | format. For the omitted details we follow the "JFIF" conventions, revision |
| 239 | 1.02. A copy of the JFIF spec is available from: |
| 240 | Literature Department |
| 241 | C-Cube Microsystems, Inc. |
| 242 | 1778 McCarthy Blvd. |
| 243 | Milpitas, CA 95035 |
| 244 | phone (408) 944-6300, fax (408) 944-6314 |
| 245 | A PostScript version of this document is available at ftp.uu.net, file |
| 246 | graphics/jpeg/jfif.ps.gz. It can also be obtained by e-mail from the C-Cube |
| 247 | mail server, netlib@c3.pla.ca.us. Send the message "send jfif_ps from jpeg" |
| 248 | to the server to obtain the JFIF document; send the message "help" if you have |
| 249 | trouble. |
| 250 | |
| 251 | The TIFF 6.0 file format specification can be obtained by FTP from sgi.com |
| 252 | (192.48.153.1), file graphics/tiff/TIFF6.ps.Z; or you can order a printed copy |
| 253 | from Aldus Corp. at (206) 628-6593. It should be noted that the TIFF 6.0 spec |
| 254 | of 3-June-92 has a number of serious problems in its JPEG features. A |
| 255 | redesign effort is currently underway to correct these problems; it is |
| 256 | expected to result in a new, incompatible, spec. IJG intends to support the |
| 257 | corrected version of TIFF when the new spec is issued. |
| 258 | |
| 259 | |
| 260 | ARCHIVE LOCATIONS |
| 261 | ================= |
| 262 | |
| 263 | The "official" archive site for this software is ftp.uu.net (Internet |
| 264 | address 192.48.96.9). The most recent released version can always be found |
| 265 | there in directory graphics/jpeg. This particular version will be archived |
Thomas G. Lane | 9ba2f5e | 1994-12-07 00:00:00 +0000 | [diff] [blame^] | 266 | as graphics/jpeg/jpegsrc.v5a.tar.gz. If you are on the Internet, you |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 267 | can retrieve files from ftp.uu.net by standard anonymous FTP. If you don't |
| 268 | have FTP access, UUNET's archives are also available via UUCP; contact |
| 269 | help@uunet.uu.net for information on retrieving files that way. |
| 270 | |
| 271 | Numerous Internet sites maintain copies of the UUNET files; in particular, |
| 272 | you can probably find a copy at any site that archives comp.sources.misc |
| 273 | submissions. However, only ftp.uu.net is guaranteed to have the latest |
| 274 | official version. |
| 275 | |
Thomas G. Lane | 9ba2f5e | 1994-12-07 00:00:00 +0000 | [diff] [blame^] | 276 | You can also obtain this software from CompuServe, in the GRAPHSUPPORT |
| 277 | forum (GO GRAPHSUP), probably in library 15 (there are rumors of a pending |
| 278 | reorganization there). Again, CompuServe is not guaranteed to have the |
| 279 | very latest version. |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 280 | |
| 281 | The JPEG FAQ (Frequently Asked Questions) article is a useful source of |
Thomas G. Lane | 9ba2f5e | 1994-12-07 00:00:00 +0000 | [diff] [blame^] | 282 | general information about JPEG. It is updated constantly and therefore is |
| 283 | not included in this distribution. The FAQ is posted every two weeks to |
| 284 | Usenet newsgroups comp.graphics, news.answers, and other groups. You can |
| 285 | always obtain the latest version from the news.answers archive at |
| 286 | rtfm.mit.edu. By FTP, fetch /pub/usenet/news.answers/jpeg-faq/part1 and |
| 287 | .../part2. If you don't have FTP, send e-mail to mail-server@rtfm.mit.edu |
| 288 | with body |
| 289 | send usenet/news.answers/jpeg-faq/part1 |
| 290 | send usenet/news.answers/jpeg-faq/part2 |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 291 | |
| 292 | |
| 293 | RELATED SOFTWARE |
| 294 | ================ |
| 295 | |
| 296 | Numerous viewing and image manipulation programs now support JPEG. (Quite a |
| 297 | few of them use this library to do so.) The JPEG FAQ described above lists |
| 298 | some of the more popular free and shareware viewers, and tells where to |
| 299 | obtain them on Internet. |
| 300 | |
| 301 | If you are on a Unix machine, we highly recommend Jef Poskanzer's free |
| 302 | PBMPLUS image software, which provides many useful operations on PPM-format |
| 303 | image files. In particular, it can convert PPM images to and from a wide |
| 304 | range of other formats. You can obtain this package by FTP from ftp.x.org |
| 305 | (contrib/pbmplus*.tar.Z) or ftp.ee.lbl.gov (pbmplus*.tar.Z). There is also |
| 306 | a newer update of this package called NETPBM, available from |
| 307 | wuarchive.wustl.edu under directory /graphics/graphics/packages/NetPBM/. |
| 308 | Unfortunately PBMPLUS/NETPBM is not nearly as portable as the IJG software |
| 309 | is; you are likely to have difficulty making it work on any non-Unix machine. |
| 310 | |
| 311 | A different free JPEG implementation, written by the PVRG group at Stanford, |
| 312 | is available from havefun.stanford.edu in directory pub/jpeg. This program |
| 313 | is designed for research and experimentation rather than production use; |
| 314 | it is slower, harder to use, and less portable than the IJG code, but it |
| 315 | implements a larger subset of the JPEG standard. In particular, it supports |
| 316 | lossless JPEG. |
| 317 | |
| 318 | |
| 319 | FILE FORMAT WARS |
| 320 | ================ |
| 321 | |
| 322 | Some JPEG programs produce files that are not compatible with our library. |
| 323 | The root of the problem is that the ISO JPEG committee failed to specify a |
| 324 | concrete file format. Some vendors "filled in the blanks" on their own, |
| 325 | creating proprietary formats that no one else could read. (For example, none |
| 326 | of the early commercial JPEG implementations for the Macintosh were able to |
| 327 | exchange compressed files.) |
| 328 | |
| 329 | The file format we have adopted is called JFIF (see REFERENCES). This format |
| 330 | has been agreed to by a number of major commercial JPEG vendors, and it has |
| 331 | become the de facto standard. JFIF is a minimal or "low end" representation. |
| 332 | Work is also going forward to incorporate JPEG compression into the TIFF |
| 333 | standard, for use in "high end" applications that need to record a lot of |
| 334 | additional data about an image. We intend to support TIFF in the future. |
| 335 | We hope that these two formats will be sufficient and that other, |
| 336 | incompatible JPEG file formats will not proliferate. |
| 337 | |
| 338 | Indeed, part of the reason for developing and releasing this free software is |
| 339 | to help force rapid convergence to de facto standards for JPEG file formats. |
| 340 | SUPPORT STANDARD, NON-PROPRIETARY FORMATS: demand JFIF or TIFF/JPEG! |
| 341 | |
| 342 | |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 343 | TO DO |
| 344 | ===== |
| 345 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 346 | In future versions, we are considering supporting progressive JPEG |
| 347 | compression, the upcoming JPEG Part 3 extensions, and other improvements. |
Thomas G. Lane | 88aeed4 | 1992-12-10 00:00:00 +0000 | [diff] [blame] | 348 | |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 349 | As always, speeding things up is high on our priority list. |
Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame] | 350 | |
| 351 | Please send bug reports, offers of help, etc. to jpeg-info@uunet.uu.net. |