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| 1 : | chl | 1.1 | The Independent JPEG Group's JPEG software |
| 2 : | ========================================== | ||
| 3 : | |||
| 4 : | README for release 6b of 27-Mar-1998 | ||
| 5 : | ==================================== | ||
| 6 : | |||
| 7 : | This distribution contains the sixth 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 : | Serious users of this software (particularly those incorporating it into | ||
| 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. | ||
| 15 : | |||
| 16 : | This software is the work of Tom Lane, Philip Gladstone, Jim Boucher, | ||
| 17 : | Lee Crocker, Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, | ||
| 18 : | Guido Vollbeding, Ge' Weijers, and other members of the Independent JPEG | ||
| 19 : | Group. | ||
| 20 : | |||
| 21 : | IJG is not affiliated with the official ISO JPEG standards committee. | ||
| 22 : | |||
| 23 : | |||
| 24 : | DOCUMENTATION ROADMAP | ||
| 25 : | ===================== | ||
| 26 : | |||
| 27 : | This file contains the following sections: | ||
| 28 : | |||
| 29 : | OVERVIEW General description of JPEG and the IJG software. | ||
| 30 : | LEGAL ISSUES Copyright, lack of warranty, terms of distribution. | ||
| 31 : | REFERENCES Where to learn more about JPEG. | ||
| 32 : | ARCHIVE LOCATIONS Where to find newer versions of this software. | ||
| 33 : | RELATED SOFTWARE Other stuff you should get. | ||
| 34 : | FILE FORMAT WARS Software *not* to get. | ||
| 35 : | TO DO Plans for future IJG releases. | ||
| 36 : | |||
| 37 : | Other documentation files in the distribution are: | ||
| 38 : | |||
| 39 : | User documentation: | ||
| 40 : | install.doc How to configure and install the IJG software. | ||
| 41 : | usage.doc Usage instructions for cjpeg, djpeg, jpegtran, | ||
| 42 : | rdjpgcom, and wrjpgcom. | ||
| 43 : | *.1 Unix-style man pages for programs (same info as usage.doc). | ||
| 44 : | wizard.doc Advanced usage instructions for JPEG wizards only. | ||
| 45 : | change.log Version-to-version change highlights. | ||
| 46 : | Programmer and internal documentation: | ||
| 47 : | libjpeg.doc How to use the JPEG library in your own programs. | ||
| 48 : | example.c Sample code for calling the JPEG library. | ||
| 49 : | structure.doc Overview of the JPEG library's internal structure. | ||
| 50 : | filelist.doc Road map of IJG files. | ||
| 51 : | coderules.doc Coding style rules --- please read if you contribute code. | ||
| 52 : | |||
| 53 : | Please read at least the files install.doc and usage.doc. Useful information | ||
| 54 : | can also be found in the JPEG FAQ (Frequently Asked Questions) article. See | ||
| 55 : | ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. | ||
| 56 : | |||
| 57 : | If you want to understand how the JPEG code works, we suggest reading one or | ||
| 58 : | more of the REFERENCES, then looking at the documentation files (in roughly | ||
| 59 : | the order listed) before diving into the code. | ||
| 60 : | |||
| 61 : | |||
| 62 : | OVERVIEW | ||
| 63 : | ======== | ||
| 64 : | |||
| 65 : | This package contains C software to implement JPEG image compression and | ||
| 66 : | decompression. JPEG (pronounced "jay-peg") is a standardized compression | ||
| 67 : | method for full-color and gray-scale images. JPEG is intended for compressing | ||
| 68 : | "real-world" scenes; line drawings, cartoons and other non-realistic images | ||
| 69 : | are not its strong suit. JPEG is lossy, meaning that the output image is not | ||
| 70 : | exactly identical to the input image. Hence you must not use JPEG if you | ||
| 71 : | have to have identical output bits. However, on typical photographic images, | ||
| 72 : | very good compression levels can be obtained with no visible change, and | ||
| 73 : | remarkably high compression levels are possible if you can tolerate a | ||
| 74 : | low-quality image. For more details, see the references, or just experiment | ||
| 75 : | with various compression settings. | ||
| 76 : | |||
| 77 : | This software implements JPEG baseline, extended-sequential, and progressive | ||
| 78 : | compression processes. Provision is made for supporting all variants of these | ||
| 79 : | processes, although some uncommon parameter settings aren't implemented yet. | ||
| 80 : | For legal reasons, we are not distributing code for the arithmetic-coding | ||
| 81 : | variants of JPEG; see LEGAL ISSUES. We have made no provision for supporting | ||
| 82 : | the hierarchical or lossless processes defined in the standard. | ||
| 83 : | |||
| 84 : | We provide a set of library routines for reading and writing JPEG image files, | ||
| 85 : | plus two sample applications "cjpeg" and "djpeg", which use the library to | ||
| 86 : | perform conversion between JPEG and some other popular image file formats. | ||
| 87 : | The library is intended to be reused in other applications. | ||
| 88 : | |||
| 89 : | In order to support file conversion and viewing software, we have included | ||
| 90 : | considerable functionality beyond the bare JPEG coding/decoding capability; | ||
| 91 : | for example, the color quantization modules are not strictly part of JPEG | ||
| 92 : | decoding, but they are essential for output to colormapped file formats or | ||
| 93 : | colormapped displays. These extra functions can be compiled out of the | ||
| 94 : | library if not required for a particular application. We have also included | ||
| 95 : | "jpegtran", a utility for lossless transcoding between different JPEG | ||
| 96 : | processes, and "rdjpgcom" and "wrjpgcom", two simple applications for | ||
| 97 : | inserting and extracting textual comments in JFIF files. | ||
| 98 : | |||
| 99 : | The emphasis in designing this software has been on achieving portability and | ||
| 100 : | flexibility, while also making it fast enough to be useful. In particular, | ||
| 101 : | the software is not intended to be read as a tutorial on JPEG. (See the | ||
| 102 : | REFERENCES section for introductory material.) Rather, it is intended to | ||
| 103 : | be reliable, portable, industrial-strength code. We do not claim to have | ||
| 104 : | achieved that goal in every aspect of the software, but we strive for it. | ||
| 105 : | |||
| 106 : | We welcome the use of this software as a component of commercial products. | ||
| 107 : | No royalty is required, but we do ask for an acknowledgement in product | ||
| 108 : | documentation, as described under LEGAL ISSUES. | ||
| 109 : | |||
| 110 : | |||
| 111 : | LEGAL ISSUES | ||
| 112 : | ============ | ||
| 113 : | |||
| 114 : | In plain English: | ||
| 115 : | |||
| 116 : | 1. We don't promise that this software works. (But if you find any bugs, | ||
| 117 : | please let us know!) | ||
| 118 : | 2. You can use this software for whatever you want. You don't have to pay us. | ||
| 119 : | 3. You may not pretend that you wrote this software. If you use it in a | ||
| 120 : | program, you must acknowledge somewhere in your documentation that | ||
| 121 : | you've used the IJG code. | ||
| 122 : | |||
| 123 : | In legalese: | ||
| 124 : | |||
| 125 : | The authors make NO WARRANTY or representation, either express or implied, | ||
| 126 : | with respect to this software, its quality, accuracy, merchantability, or | ||
| 127 : | fitness for a particular purpose. This software is provided "AS IS", and you, | ||
| 128 : | its user, assume the entire risk as to its quality and accuracy. | ||
| 129 : | |||
| 130 : | This software is copyright (C) 1991-1998, Thomas G. Lane. | ||
| 131 : | All Rights Reserved except as specified below. | ||
| 132 : | |||
| 133 : | Permission is hereby granted to use, copy, modify, and distribute this | ||
| 134 : | software (or portions thereof) for any purpose, without fee, subject to these | ||
| 135 : | conditions: | ||
| 136 : | (1) If any part of the source code for this software is distributed, then this | ||
| 137 : | README file must be included, with this copyright and no-warranty notice | ||
| 138 : | unaltered; and any additions, deletions, or changes to the original files | ||
| 139 : | must be clearly indicated in accompanying documentation. | ||
| 140 : | (2) If only executable code is distributed, then the accompanying | ||
| 141 : | documentation must state that "this software is based in part on the work of | ||
| 142 : | the Independent JPEG Group". | ||
| 143 : | (3) Permission for use of this software is granted only if the user accepts | ||
| 144 : | full responsibility for any undesirable consequences; the authors accept | ||
| 145 : | NO LIABILITY for damages of any kind. | ||
| 146 : | |||
| 147 : | These conditions apply to any software derived from or based on the IJG code, | ||
| 148 : | not just to the unmodified library. If you use our work, you ought to | ||
| 149 : | acknowledge us. | ||
| 150 : | |||
| 151 : | Permission is NOT granted for the use of any IJG author's name or company name | ||
| 152 : | in advertising or publicity relating to this software or products derived from | ||
| 153 : | it. This software may be referred to only as "the Independent JPEG Group's | ||
| 154 : | software". | ||
| 155 : | |||
| 156 : | We specifically permit and encourage the use of this software as the basis of | ||
| 157 : | commercial products, provided that all warranty or liability claims are | ||
| 158 : | assumed by the product vendor. | ||
| 159 : | |||
| 160 : | |||
| 161 : | ansi2knr.c is included in this distribution by permission of L. Peter Deutsch, | ||
| 162 : | sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA. | ||
| 163 : | ansi2knr.c is NOT covered by the above copyright and conditions, but instead | ||
| 164 : | by the usual distribution terms of the Free Software Foundation; principally, | ||
| 165 : | that you must include source code if you redistribute it. (See the file | ||
| 166 : | ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part | ||
| 167 : | of any program generated from the IJG code, this does not limit you more than | ||
| 168 : | the foregoing paragraphs do. | ||
| 169 : | |||
| 170 : | The Unix configuration script "configure" was produced with GNU Autoconf. | ||
| 171 : | It is copyright by the Free Software Foundation but is freely distributable. | ||
| 172 : | The same holds for its supporting scripts (config.guess, config.sub, | ||
| 173 : | ltconfig, ltmain.sh). Another support script, install-sh, is copyright | ||
| 174 : | by M.I.T. but is also freely distributable. | ||
| 175 : | |||
| 176 : | It appears that the arithmetic coding option of the JPEG spec is covered by | ||
| 177 : | patents owned by IBM, AT&T, and Mitsubishi. Hence arithmetic coding cannot | ||
| 178 : | legally be used without obtaining one or more licenses. For this reason, | ||
| 179 : | support for arithmetic coding has been removed from the free JPEG software. | ||
| 180 : | (Since arithmetic coding provides only a marginal gain over the unpatented | ||
| 181 : | Huffman mode, it is unlikely that very many implementations will support it.) | ||
| 182 : | So far as we are aware, there are no patent restrictions on the remaining | ||
| 183 : | code. | ||
| 184 : | |||
| 185 : | The IJG distribution formerly included code to read and write GIF files. | ||
| 186 : | To avoid entanglement with the Unisys LZW patent, GIF reading support has | ||
| 187 : | been removed altogether, and the GIF writer has been simplified to produce | ||
| 188 : | "uncompressed GIFs". This technique does not use the LZW algorithm; the | ||
| 189 : | resulting GIF files are larger than usual, but are readable by all standard | ||
| 190 : | GIF decoders. | ||
| 191 : | |||
| 192 : | We are required to state that | ||
| 193 : | "The Graphics Interchange Format(c) is the Copyright property of | ||
| 194 : | CompuServe Incorporated. GIF(sm) is a Service Mark property of | ||
| 195 : | CompuServe Incorporated." | ||
| 196 : | |||
| 197 : | |||
| 198 : | REFERENCES | ||
| 199 : | ========== | ||
| 200 : | |||
| 201 : | We highly recommend reading one or more of these references before trying to | ||
| 202 : | understand the innards of the JPEG software. | ||
| 203 : | |||
| 204 : | The best short technical introduction to the JPEG compression algorithm is | ||
| 205 : | Wallace, Gregory K. "The JPEG Still Picture Compression Standard", | ||
| 206 : | Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. | ||
| 207 : | (Adjacent articles in that issue discuss MPEG motion picture compression, | ||
| 208 : | applications of JPEG, and related topics.) If you don't have the CACM issue | ||
| 209 : | handy, a PostScript file containing a revised version of Wallace's article is | ||
| 210 : | available at ftp://ftp.uu.net/graphics/jpeg/wallace.ps.gz. The file (actually | ||
| 211 : | a preprint for an article that appeared in IEEE Trans. Consumer Electronics) | ||
| 212 : | omits the sample images that appeared in CACM, but it includes corrections | ||
| 213 : | and some added material. Note: the Wallace article is copyright ACM and IEEE, | ||
| 214 : | and it may not be used for commercial purposes. | ||
| 215 : | |||
| 216 : | A somewhat less technical, more leisurely introduction to JPEG can be found in | ||
| 217 : | "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by | ||
| 218 : | M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides | ||
| 219 : | good explanations and example C code for a multitude of compression methods | ||
| 220 : | including JPEG. It is an excellent source if you are comfortable reading C | ||
| 221 : | code but don't know much about data compression in general. The book's JPEG | ||
| 222 : | sample code is far from industrial-strength, but when you are ready to look | ||
| 223 : | at a full implementation, you've got one here... | ||
| 224 : | |||
| 225 : | The best full description of JPEG is the textbook "JPEG Still Image Data | ||
| 226 : | Compression Standard" by William B. Pennebaker and Joan L. Mitchell, published | ||
| 227 : | by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. Price US$59.95, 638 pp. | ||
| 228 : | The book includes the complete text of the ISO JPEG standards (DIS 10918-1 | ||
| 229 : | and draft DIS 10918-2). This is by far the most complete exposition of JPEG | ||
| 230 : | in existence, and we highly recommend it. | ||
| 231 : | |||
| 232 : | The JPEG standard itself is not available electronically; you must order a | ||
| 233 : | paper copy through ISO or ITU. (Unless you feel a need to own a certified | ||
| 234 : | official copy, we recommend buying the Pennebaker and Mitchell book instead; | ||
| 235 : | it's much cheaper and includes a great deal of useful explanatory material.) | ||
| 236 : | In the USA, copies of the standard may be ordered from ANSI Sales at (212) | ||
| 237 : | 642-4900, or from Global Engineering Documents at (800) 854-7179. (ANSI | ||
| 238 : | doesn't take credit card orders, but Global does.) It's not cheap: as of | ||
| 239 : | 1992, ANSI was charging $95 for Part 1 and $47 for Part 2, plus 7% | ||
| 240 : | shipping/handling. The standard is divided into two parts, Part 1 being the | ||
| 241 : | actual specification, while Part 2 covers compliance testing methods. Part 1 | ||
| 242 : | is titled "Digital Compression and Coding of Continuous-tone Still Images, | ||
| 243 : | Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS | ||
| 244 : | 10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of | ||
| 245 : | Continuous-tone Still Images, Part 2: Compliance testing" and has document | ||
| 246 : | numbers ISO/IEC IS 10918-2, ITU-T T.83. | ||
| 247 : | |||
| 248 : | Some extensions to the original JPEG standard are defined in JPEG Part 3, | ||
| 249 : | a newer ISO standard numbered ISO/IEC IS 10918-3 and ITU-T T.84. IJG | ||
| 250 : | currently does not support any Part 3 extensions. | ||
| 251 : | |||
| 252 : | The JPEG standard does not specify all details of an interchangeable file | ||
| 253 : | format. For the omitted details we follow the "JFIF" conventions, revision | ||
| 254 : | 1.02. A copy of the JFIF spec is available from: | ||
| 255 : | Literature Department | ||
| 256 : | C-Cube Microsystems, Inc. | ||
| 257 : | 1778 McCarthy Blvd. | ||
| 258 : | Milpitas, CA 95035 | ||
| 259 : | phone (408) 944-6300, fax (408) 944-6314 | ||
| 260 : | A PostScript version of this document is available by FTP at | ||
| 261 : | ftp://ftp.uu.net/graphics/jpeg/jfif.ps.gz. There is also a plain text | ||
| 262 : | version at ftp://ftp.uu.net/graphics/jpeg/jfif.txt.gz, but it is missing | ||
| 263 : | the figures. | ||
| 264 : | |||
| 265 : | The TIFF 6.0 file format specification can be obtained by FTP from | ||
| 266 : | ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme | ||
| 267 : | found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. | ||
| 268 : | IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). | ||
| 269 : | Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 | ||
| 270 : | (Compression tag 7). Copies of this Note can be obtained from ftp.sgi.com or | ||
| 271 : | from ftp://ftp.uu.net/graphics/jpeg/. It is expected that the next revision | ||
| 272 : | of the TIFF spec will replace the 6.0 JPEG design with the Note's design. | ||
| 273 : | Although IJG's own code does not support TIFF/JPEG, the free libtiff library | ||
| 274 : | uses our library to implement TIFF/JPEG per the Note. libtiff is available | ||
| 275 : | from ftp://ftp.sgi.com/graphics/tiff/. | ||
| 276 : | |||
| 277 : | |||
| 278 : | ARCHIVE LOCATIONS | ||
| 279 : | ================= | ||
| 280 : | |||
| 281 : | The "official" archive site for this software is ftp.uu.net (Internet | ||
| 282 : | address 192.48.96.9). The most recent released version can always be found | ||
| 283 : | there in directory graphics/jpeg. This particular version will be archived | ||
| 284 : | as ftp://ftp.uu.net/graphics/jpeg/jpegsrc.v6b.tar.gz. If you don't have | ||
| 285 : | direct Internet access, UUNET's archives are also available via UUCP; contact | ||
| 286 : | help@uunet.uu.net for information on retrieving files that way. | ||
| 287 : | |||
| 288 : | Numerous Internet sites maintain copies of the UUNET files. However, only | ||
| 289 : | ftp.uu.net is guaranteed to have the latest official version. | ||
| 290 : | |||
| 291 : | You can also obtain this software in DOS-compatible "zip" archive format from | ||
| 292 : | the SimTel archives (ftp://ftp.simtel.net/pub/simtelnet/msdos/graphics/), or | ||
| 293 : | on CompuServe in the Graphics Support forum (GO CIS:GRAPHSUP), library 12 | ||
| 294 : | "JPEG Tools". Again, these versions may sometimes lag behind the ftp.uu.net | ||
| 295 : | release. | ||
| 296 : | |||
| 297 : | The JPEG FAQ (Frequently Asked Questions) article is a useful source of | ||
| 298 : | general information about JPEG. It is updated constantly and therefore is | ||
| 299 : | not included in this distribution. The FAQ is posted every two weeks to | ||
| 300 : | Usenet newsgroups comp.graphics.misc, news.answers, and other groups. | ||
| 301 : | It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ | ||
| 302 : | and other news.answers archive sites, including the official news.answers | ||
| 303 : | archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. | ||
| 304 : | If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu | ||
| 305 : | with body | ||
| 306 : | send usenet/news.answers/jpeg-faq/part1 | ||
| 307 : | send usenet/news.answers/jpeg-faq/part2 | ||
| 308 : | |||
| 309 : | |||
| 310 : | RELATED SOFTWARE | ||
| 311 : | ================ | ||
| 312 : | |||
| 313 : | Numerous viewing and image manipulation programs now support JPEG. (Quite a | ||
| 314 : | few of them use this library to do so.) The JPEG FAQ described above lists | ||
| 315 : | some of the more popular free and shareware viewers, and tells where to | ||
| 316 : | obtain them on Internet. | ||
| 317 : | |||
| 318 : | If you are on a Unix machine, we highly recommend Jef Poskanzer's free | ||
| 319 : | PBMPLUS software, which provides many useful operations on PPM-format image | ||
| 320 : | files. In particular, it can convert PPM images to and from a wide range of | ||
| 321 : | other formats, thus making cjpeg/djpeg considerably more useful. The latest | ||
| 322 : | version is distributed by the NetPBM group, and is available from numerous | ||
| 323 : | sites, notably ftp://wuarchive.wustl.edu/graphics/graphics/packages/NetPBM/. | ||
| 324 : | Unfortunately PBMPLUS/NETPBM is not nearly as portable as the IJG software is; | ||
| 325 : | you are likely to have difficulty making it work on any non-Unix machine. | ||
| 326 : | |||
| 327 : | A different free JPEG implementation, written by the PVRG group at Stanford, | ||
| 328 : | is available from ftp://havefun.stanford.edu/pub/jpeg/. This program | ||
| 329 : | is designed for research and experimentation rather than production use; | ||
| 330 : | it is slower, harder to use, and less portable than the IJG code, but it | ||
| 331 : | is easier to read and modify. Also, the PVRG code supports lossless JPEG, | ||
| 332 : | which we do not. (On the other hand, it doesn't do progressive JPEG.) | ||
| 333 : | |||
| 334 : | |||
| 335 : | FILE FORMAT WARS | ||
| 336 : | ================ | ||
| 337 : | |||
| 338 : | Some JPEG programs produce files that are not compatible with our library. | ||
| 339 : | The root of the problem is that the ISO JPEG committee failed to specify a | ||
| 340 : | concrete file format. Some vendors "filled in the blanks" on their own, | ||
| 341 : | creating proprietary formats that no one else could read. (For example, none | ||
| 342 : | of the early commercial JPEG implementations for the Macintosh were able to | ||
| 343 : | exchange compressed files.) | ||
| 344 : | |||
| 345 : | The file format we have adopted is called JFIF (see REFERENCES). This format | ||
| 346 : | has been agreed to by a number of major commercial JPEG vendors, and it has | ||
| 347 : | become the de facto standard. JFIF is a minimal or "low end" representation. | ||
| 348 : | We recommend the use of TIFF/JPEG (TIFF revision 6.0 as modified by TIFF | ||
| 349 : | Technical Note #2) for "high end" applications that need to record a lot of | ||
| 350 : | additional data about an image. TIFF/JPEG is fairly new and not yet widely | ||
| 351 : | supported, unfortunately. | ||
| 352 : | |||
| 353 : | The upcoming JPEG Part 3 standard defines a file format called SPIFF. | ||
| 354 : | SPIFF is interoperable with JFIF, in the sense that most JFIF decoders should | ||
| 355 : | be able to read the most common variant of SPIFF. SPIFF has some technical | ||
| 356 : | advantages over JFIF, but its major claim to fame is simply that it is an | ||
| 357 : | official standard rather than an informal one. At this point it is unclear | ||
| 358 : | whether SPIFF will supersede JFIF or whether JFIF will remain the de-facto | ||
| 359 : | standard. IJG intends to support SPIFF once the standard is frozen, but we | ||
| 360 : | have not decided whether it should become our default output format or not. | ||
| 361 : | (In any case, our decoder will remain capable of reading JFIF indefinitely.) | ||
| 362 : | |||
| 363 : | Various proprietary file formats incorporating JPEG compression also exist. | ||
| 364 : | We have little or no sympathy for the existence of these formats. Indeed, | ||
| 365 : | one of the original reasons for developing this free software was to help | ||
| 366 : | force convergence on common, open format standards for JPEG files. Don't | ||
| 367 : | use a proprietary file format! | ||
| 368 : | |||
| 369 : | |||
| 370 : | TO DO | ||
| 371 : | ===== | ||
| 372 : | |||
| 373 : | The major thrust for v7 will probably be improvement of visual quality. | ||
| 374 : | The current method for scaling the quantization tables is known not to be | ||
| 375 : | very good at low Q values. We also intend to investigate block boundary | ||
| 376 : | smoothing, "poor man's variable quantization", and other means of improving | ||
| 377 : | quality-vs-file-size performance without sacrificing compatibility. | ||
| 378 : | |||
| 379 : | In future versions, we are considering supporting some of the upcoming JPEG | ||
| 380 : | Part 3 extensions --- principally, variable quantization and the SPIFF file | ||
| 381 : | format. | ||
| 382 : | |||
| 383 : | As always, speeding things up is of great interest. | ||
| 384 : | |||
| 385 : | Please send bug reports, offers of help, etc. to jpeg-info@uunet.uu.net. |
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