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The Independent JPEG Group's JPEG software
==========================================
README for release 3 of 17-Mar-92
==================================
This distribution contains the third official 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.
For installation instructions, see file SETUP; for usage instructions, see
file USAGE (or the cjpeg.1 and djpeg.1 manual pages).
This software is still undergoing revision. Updated versions may be obtained
by FTP or UUCP to UUNET and other archive sites; see ARCHIVE LOCATIONS below
for details.
If you intend to become a serious user of this software, please contact
jpeg-info@uunet.uu.net to be added to our electronic mailing list. Then
you'll be notified of updates and have a chance to participate in discussions,
etc.
This software is the work of Tom Lane, Philip Gladstone, Luis Ortiz,
Lee Crocker, Ge' Weijers, and other members of the Independent JPEG Group.
DISCLAIMER
==========
THIS SOFTWARE IS NOT COMPLETE NOR FULLY DEBUGGED. It is not guaranteed to be
useful for anything, nor to be compatible with subsequent releases, nor to be
an accurate implementation of the JPEG standard. (See LEGAL ISSUES for even
more disclaimers.)
Please report any problems with this software to jpeg-info@uunet.uu.net.
WHAT'S HERE
===========
This distribution contains C software to implement JPEG image compression and
decompression. JPEG (pronounced "jay-peg") is a standardized compression
method for full-color and gray-scale images. JPEG is intended for
"real-world" scenes; cartoons and other non-realistic images are not its
strong suit. JPEG is lossy, meaning that the output image is not necessarily
identical to the input image. Hence you should not use JPEG if you have to
have identical output bits. However, on typical images of real-world scenes,
very good compression levels can be obtained with no visible change, and
amazingly high compression levels can be obtained if you can tolerate a
low-quality image. For more details, see the references, or just experiment
with various compression settings.
The software implements JPEG baseline and extended-sequential compression
processes. Provision is made for supporting all variants of these processes,
although some uncommon parameter settings aren't implemented yet. For legal
reasons, we are not distributing code for the arithmetic-coding process; see
LEGAL ISSUES. At present we have made no provision for supporting the
progressive, hierarchical, or lossless processes defined in the standard.
The present software is not far beyond the prototype stage. It does not
support all possible variants of the JPEG standard, and some functions have
rather slow and/or crude implementations. However, it is useful already.
The emphasis in designing this software has been on achieving portability and
flexibility, while also making it fast enough to be useful. We have not yet
undertaken serious performance measurement or tuning; we intend to do so in
the future.
This software can be used on several levels:
* As canned software for JPEG compression and decompression. Just edit the
Makefile and configuration files as needed (see file SETUP), compile and go.
Members of the Independent JPEG Group will improve the out-of-the-box
functionality and speed as time goes on.
* As the basis for other JPEG programs. For example, you could incorporate
the decompressor into a general image viewing package by replacing the
output module with write-to-screen functions. For an implementation on
specific hardware, you might want to replace some of the inner loops with
assembly code. For a non-command-line-driven system, you might want a
different user interface. (Members of the group will be producing Macintosh
and Amiga versions with more appropriate user interfaces, for example.)
* As a toolkit for experimentation with JPEG and JPEG-like algorithms. Most
of the individual decisions you might want to mess with are packaged up into
separate modules. For example, the details of color-space conversion and
subsampling techniques are each localized in one compressor and one
decompressor module. You'd probably also want to extend the user interface
to give you more detailed control over the JPEG compression parameters.
In particular, we welcome the use of this software as a component of commercial
products; no royalty is required.
ARCHIVE LOCATIONS
=================
The "official" archive site for this software is ftp.uu.net (Internet
address 137.39.1.9 or 192.48.96.9). The most recent released version can
always be found there in directory graphics/jpeg. This particular version
will be archived as jpegsrc.v3.tar.Z. If you are on the Internet, you can
retrieve files from UUNET by anonymous FTP. If you don't have FTP access,
UUNET's archives are also available via UUCP; contact postmaster@uunet.uu.net
for information on retrieving files that way.
Various other Internet sites maintain copies of the UUNET file, which may or
may not be up-to-date. In Europe, try nic.funet.fi (128.214.6.100; look in
directory pub/graphics/programs/jpeg).
You can also obtain this software from CompuServe, in the GRAPHSUPPORT forum
(GO PICS), library 10; this version will be file jpsrc3.zip.
If you are not reasonably handy at configuring and installing portable C
programs, you may have some difficulty installing this package. You may
prefer to obtain a pre-built executable version. A collection of pre-built
executables for various machines is currently available for anonymous FTP at
procyon.cis.ksu.edu (129.130.10.80 --- this number is due to change soon);
look under /pub/JPEG. The administrators of this system ask that FTP traffic
be limited to non-prime hours. For more information on this archive, please
contact Steve Davis (strat@cis.ksu.edu). This collection is not maintained by
the Independent JPEG Group, and programs in it may not be the latest version.
SUPPORTING SOFTWARE
===================
You will probably want Jef Poskanzer's PBMPLUS image software, which provides
many useful operations on PPM-format image files. In particular, it can
convert PPM images to and from a wide range of other formats. You can FTP
this free software from export.lcs.mit.edu (contrib/pbmplus*.tar.Z) or
ftp.ee.lbl.gov (pbmplus*.tar.Z). Unfortunately PBMPLUS is not nearly as
portable as the JPEG software is; you are likely to have difficulty making it
work on any non-Unix machine.
If you are using X Windows you might want to use the xv or xloadimage viewers
to save yourself the trouble of converting PPM to some other format. Both of
these can be found in the contrib directory at export.lcs.mit.edu. Actually,
xv version 2.00 and up incorporates our software and thus can read and write
JPEG files directly. (NOTE: since xv internally reduces all images to 8
bits/pixel, a JPEG file written by xv will not be very high quality; you may
also prefer xloadimage for viewing if you have a 24-bit display. Caveat user.)
For DOS machines, Lee Crocker's free Piclab program is a useful companion to
the JPEG software. The latest version, currently 1.91, is available by FTP
from SIMTEL20 and its various mirror sites, file <msdos.graphics>piclb191.zip.
CompuServe also has it, in the same library as the JPEG software.
SOFTWARE THAT'S NO HELP AT ALL
==============================
Handmade Software's shareware PC program GIF2JPG produces files that are
totally incompatible with our programs. They use a proprietary format that is
an amalgam of GIF and JPEG representations. However, you can force GIF2JPG
to produce compatible files with its -j switch, and their decompression
program JPG2GIF can read our files (at least ones produced with our default
option settings).
Unfortunately, many commercial JPEG implementations are also incompatible as
of this writing, especially programs released before summer 1991. The root of
the problem is that the ISO JPEG committee failed to specify a concrete file
format. Some vendors "filled in the blanks" on their own, creating
proprietary formats that no one else could read. (For example, none of the
early commercial JPEG implementations for the Macintosh were able to exchange
compressed files.)
The file format we have adopted is called JFIF (see REFERENCES). This format
has been agreed to by a number of major commercial JPEG vendors, and we expect
that it will become the de facto standard. JFIF is a minimal representation;
work is also going forward to incorporate JPEG compression into the TIFF
standard, for use in "high end" applications that need to record a lot of
additional data about an image. We intend to support JPEG-in-TIFF in the
future. We hope that these two formats will be sufficient and that other,
incompatible JPEG file formats will not proliferate.
Indeed, part of the reason for developing and releasing this free software is
to help force rapid convergence to de facto standards for JPEG file formats.
SUPPORT STANDARD, NON-PROPRIETARY FORMATS: demand JFIF or JPEG-in-TIFF!
USING JPEG AS A SUBROUTINE IN A LARGER PROGRAM
==============================================
You can readily incorporate the JPEG compression and decompression routines in
a larger program. The file example.c provides a skeleton of the interface
routines you'll need for this purpose. Essentially, you replace jcmain.c (for
compression) and/or jdmain.c (for decompression) with your own code. Note
that the fewer JPEG options you allow the user to twiddle, the less code you
need; all the default options are set up automatically. (Alternately, if you
know a lot about JPEG or have a special application, you may want to twiddle
the default options even more extensively than jcmain/jdmain do.)
Most likely, you will want the uncompressed image to come from memory (for
compression) or go to memory or the screen (for decompression). For this
purpose you must provide image reading or writing routines that match the
interface used by the image file I/O modules (jrdXXX or jwrXXX); again,
example.c shows a skeleton of what is required.
By default, any error detected inside the JPEG routines will cause a message
to be printed on stderr, followed by exit(). You can override this behavior
by supplying your own message-printing and/or error-exit routines; again,
example.c shows how.
Mechanics: we recommend you create libjpeg.a as shown in the Makefile, then
link that with your surrounding program. (If your linker is at all
reasonable, only the code you actually need will get loaded.) Include the
files jconfig.h and jpegdata.h in C files that need to call the JPEG routines.
CAUTION: some people have tried to compile JPEG and their surrounding code
with different compilers, e.g., cc for JPEG and c++ or gcc for the rest. This
is a Real Bad Move and you will deserve what happens to you if you try it.
(Hint: the parameter structures can get laid out differently with no warning.)
Read our "architecture" file for more info. If it seems to you that the
software structure doesn't accommodate what you want to do, please contact
the authors.
Beginning with version 3, we will endeavor to hold the interface described by
example.c constant, so that you can plug in updated versions of the JPEG code
just by recompiling. However, we can't guarantee this, especially if you
choose to twiddle any JPEG options not listed in example.c. Check the
CHANGELOG when installing any new version, and compare example.c against the
prior version. Recompile your calling software (don't just relink), as we may
add or subtract fields in the parameter structures.
REFERENCES
==========
The best and most readily available introduction to the JPEG compression
algorithm is Wallace's article in the April '91 CACM:
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.) We highly recommend reading that
article before trying to understand the innards of any JPEG software.
If you don't have the CACM issue handy, a PostScript file containing a revised
version of the article is available at ftp.uu.net, graphics/jpeg/wallace.ps.Z.
The file (actually a preprint for an article to appear 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.
For more detail about the JPEG standard you pretty much have to go to the
draft standard (which is not nearly as intelligible as Wallace's article).
The standard is not now available electronically; you must order a paper copy
through ISO. In the US, copies may be ordered from ANSI Sales at (212)
642-4900. The standard is divided into two parts: Part 1 is the actual
specification, and Part 2 covers compliance testing methods. The current
"committee draft" version of Part 1 is titled "Digital Compression and Coding
of Continuous-tone Still Images, Part 1: Requirements and guidelines" and has
document number ISO/IEC CD 10918-1. (The alternate number SC2 N2215 should
also be mentioned when ordering.) This draft is expected to be superseded by
the Draft International Standard version around the end of November 1991.
Ordering info will be the same as above, but replace "CD" with "DIS" in the
document number (alternate number not yet known). The committee draft of
Part 2 is expected to be available around the end of December 1991. It will
be titled "Digital Compression and Coding of Continuous-tone Still Images,
Part 2: Compliance testing" and will have document number ISO/IEC CD 10918-2
(alternate number not yet known).
The JPEG standard does not specify all details of an interchangeable file
format. For the omitted details we follow the "JFIF" conventions, revision
1.01. A copy of the JFIF spec is available from:
Literature Department
C-Cube Microsystems, Inc.
399A West Trimble Road
San Jose, CA 95131
(408) 944-6300
The same source can supply copies of the draft JPEG-in-TIFF documents
(Appendixes O and P to the TIFF spec). PostScript versions of these
documents can also be obtained by e-mail from the C-Cube mail server,
netlib@c3.pla.ca.us. Send the message "send jfif_ps from jpeg" to obtain the
JFIF document; "send app_o_ps from jpeg" and "send app_p_ps from jpeg" will
produce the TIFF documents. Send the message "help" if you have trouble.
If you want to understand this implementation, start by reading the
"architecture" documentation file. Please read "codingrules" if you want to
contribute any code.
LEGAL ISSUES
============
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, 1992, Thomas G. Lane.
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.
Permission is NOT granted for the use of any author's name or author's 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.
ansi2knr.c is included in this distribution by permission of L. Peter Deutsch,
sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA.
ansi2knr.c is NOT covered by the above copyright and conditions, but instead
by the usual distribution terms of the Free Software Foundation; principally,
that you must include source code if you redistribute it. (See the file
ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part
of any product generated from the JPEG code, this does not limit you more than
the foregoing paragraphs do.
It appears that the arithmetic coding option of the JPEG spec is covered by
patents owned by IBM and AT&T, as well as a pending Japanese patent of
Mitsubishi. Hence arithmetic coding cannot legally be used without obtaining
one or more licenses. For this reason, support for arithmetic coding has been
removed from the free JPEG software. (Since arithmetic coding provides only a
marginal gain over the unpatented Huffman mode, it is unlikely that very many
people will choose to use it. If you do obtain the necessary licenses,
contact jpeg-info@uunet.uu.net for a copy of our arithmetic coding modules.)
So far as we are aware, there are no patent restrictions on the remaining
code.
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."
TO DO
=====
Many of the modules need fleshing out to provide more complete
implementations, or to provide faster paths for common cases.
Improving the speed will be the next big work item for the JPEG group.
We'd appreciate it if people would compile and check out the code on as wide a
variety of systems as possible, and report any portability problems
encountered (with solutions, if possible). Checks of file compatibility with
other JPEG implementations would also be of interest. Finally, we would
appreciate code profiles showing where the most time is spent, especially on
unusual systems.
Please send bug reports, offers of help, etc. to jpeg-info@uunet.uu.net.
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The Independent JPEG Group's JPEG software
==========================================
README for release 5 of 24-Sep-94
=================================
This distribution contains the fifth public release of the Independent JPEG
Group's free JPEG software. You are welcome to redistribute this software and
to use it for any purpose, subject to the conditions under LEGAL ISSUES, below.
Serious users of this software (particularly those incorporating it into
larger programs) should contact jpeg-info@uunet.uu.net to be added to our
electronic mailing list. Mailing list members are notified of updates and
have a chance to participate in technical discussions, etc.
This software is the work of Tom Lane, Philip Gladstone, Luis Ortiz, Jim
Boucher, Lee Crocker, George Phillips, Davide Rossi, Ge' Weijers, and other
members of the Independent JPEG Group.
IJG is not associated with the official ISO JPEG standards committee.
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.
RELATED SOFTWARE Other stuff you should get.
FILE FORMAT WARS Software *not* to get.
TO DO Plans for future IJG releases.
Other documentation files in the distribution are:
User documentation:
install.doc How to configure and install the IJG software.
usage.doc Usage instructions for cjpeg, djpeg, rdjpgcom, wrjpgcom.
*.1 Unix-style man pages for programs (same info as usage.doc).
change.log Version-to-version change highlights.
Programmer and internal documentation:
libjpeg.doc How to use the JPEG library in your own programs.
example.c Sample code for calling the JPEG library.
structure.doc Overview of the JPEG library's internal structure.
filelist.doc Road map of IJG files.
coderules.doc Coding style rules --- please read if you contribute code.
Please read at least the files install.doc and usage.doc. Useful 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 compression and
decompression. JPEG (pronounced "jay-peg") is a standardized compression
method for full-color and gray-scale images. JPEG is intended for compressing
"real-world" scenes; cartoons and other non-realistic images are not its
strong suit. JPEG is lossy, meaning that the output image is not necessarily
identical to the input image. Hence you must not use JPEG if you have to have
identical output bits. However, on typical images of real-world scenes, very
good compression levels can be obtained with no visible change, and amazingly
high compression levels are possible if you can tolerate a low-quality image.
For more details, see the references, or just experiment with various
compression settings.
We provide a set of library routines for reading and writing JPEG image files,
plus two simple 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.
This software implements JPEG baseline and extended-sequential compression
processes. Provision is made for supporting all variants of these processes,
although some uncommon parameter settings aren't implemented yet. For legal
reasons, we are not distributing code for the arithmetic-coding process; see
LEGAL ISSUES. At present we have made no provision for supporting the
progressive, hierarchical, or lossless processes defined in the standard.
(Support for progressive mode may be offered in a future release.)
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
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.) While we hope that the entire
package will someday be industrial-strength code, much remains to be done in
performance tuning and in improving the capabilities of individual modules.
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, 1992, 1993, 1994, Thomas G. Lane.
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.
ansi2knr.c is included in this distribution by permission of L. Peter Deutsch,
sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA.
ansi2knr.c is NOT covered by the above copyright and conditions, but instead
by the usual distribution terms of the Free Software Foundation; principally,
that you must include source code if you redistribute it. (See the file
ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part
of any program generated from the IJG code, this does not limit you more than
the foregoing paragraphs do.
The configuration script "configure" was produced by GNU Autoconf. Again,
the FSF copyright terms apply only to configure, not to the IJG code; and
again, that does not limit your use of the object code.
It appears that the arithmetic coding option of the JPEG spec is covered by
patents owned by IBM, AT&T, and Mitsubishi. Hence arithmetic coding cannot
legally be used without obtaining one or more licenses. For this reason,
support for arithmetic coding has been removed from the free JPEG software.
(Since arithmetic coding provides only a marginal gain over the unpatented
Huffman mode, it is unlikely that very many implementations will support it.)
So far as we are aware, there are no patent restrictions on the remaining
code.
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 highly 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 ftp.uu.net, graphics/jpeg/wallace.ps.gz. The file (actually a
preprint for an article to appear 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, published by M&T Books (Redwood
City, CA), 1991, ISBN 1-55851-216-0. 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 full 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). This is by far the most complete exposition of JPEG
in existence, and we highly recommend it.
The JPEG standard itself is not available electronically; you must order a
paper copy through ISO. (Unless you feel a need to own a certified official
copy, we recommend buying the Pennebaker and Mitchell book instead; it's much
cheaper and includes a great deal of useful explanatory material.) In the US,
copies of the standard may be ordered from ANSI Sales at (212) 642-4900, or
from Global Engineering Documents at (800) 854-7179. (ANSI doesn't take
credit card orders, but Global does.) It's not cheap: as of 1992, ANSI was
charging $95 for Part 1 and $47 for Part 2, plus 7% shipping/handling. The
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 number ISO/IEC IS 10918-1. As of mid-1994,
Part 2 is still at Draft International Standard status. It is titled "Digital
Compression and Coding of Continuous-tone Still Images, Part 2: Compliance
testing" and has document number ISO/IEC DIS 10918-2. (The document number
will change to IS 10918-2 when final approval is obtained.) A Part 3,
covering extensions, is likely to appear in draft form in late 1994.
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. A copy of the JFIF spec is available from:
Literature Department
C-Cube Microsystems, Inc.
1778 McCarthy Blvd.
Milpitas, CA 95035
phone (408) 944-6300, fax (408) 944-6314
A PostScript version of this document is available at ftp.uu.net, file
graphics/jpeg/jfif.ps.gz. It can also be obtained by e-mail from the C-Cube
mail server, netlib@c3.pla.ca.us. Send the message "send jfif_ps from jpeg"
to the server to obtain the JFIF document; send the message "help" if you have
trouble.
The TIFF 6.0 file format specification can be obtained by FTP from sgi.com
(192.48.153.1), file graphics/tiff/TIFF6.ps.Z; or you can order a printed copy
from Aldus Corp. at (206) 628-6593. It should be noted that the TIFF 6.0 spec
of 3-June-92 has a number of serious problems in its JPEG features. A
redesign effort is currently underway to correct these problems; it is
expected to result in a new, incompatible, spec. IJG intends to support the
corrected version of TIFF when the new spec is issued.
ARCHIVE LOCATIONS
=================
The "official" archive site for this software is ftp.uu.net (Internet
address 192.48.96.9). The most recent released version can always be found
there in directory graphics/jpeg. This particular version will be archived
as graphics/jpeg/jpegsrc.v5.tar.gz. If you are on the Internet, you
can retrieve files from ftp.uu.net by standard anonymous FTP. If you don't
have FTP access, UUNET's archives are also available via UUCP; contact
help@uunet.uu.net for information on retrieving files that way.
Numerous Internet sites maintain copies of the UUNET files; in particular,
you can probably find a copy at any site that archives comp.sources.misc
submissions. However, only ftp.uu.net is guaranteed to have the latest
official version.
You can also obtain this software from CompuServe, in the GRAPHSUPPORT forum
(GO GRAPHSUP); this version will be file jpsrc5.zip in library 15. Again,
CompuServe is not guaranteed to have the very latest version.
The JPEG FAQ (Frequently Asked Questions) article is a useful source of
general information about JPEG. It is updated constantly and therefore
is not included in this distribution. The FAQ is posted every two weeks
to Usenet newsgroups comp.graphics, news.answers, and other groups. You
can always obtain the latest version from the news.answers archive at
rtfm.mit.edu (18.181.0.24). By FTP, fetch /pub/usenet/news.answers/jpeg-faq.
If you don't have FTP, send e-mail to mail-server@rtfm.mit.edu with body
"send usenet/news.answers/jpeg-faq".
RELATED SOFTWARE
================
Numerous viewing and image manipulation programs now support JPEG. (Quite a
few of them use this library to do so.) The JPEG FAQ described above lists
some of the more popular free and shareware viewers, and tells where to
obtain them on Internet.
If you are on a Unix machine, we highly recommend Jef Poskanzer's free
PBMPLUS image software, which provides many useful operations on PPM-format
image files. In particular, it can convert PPM images to and from a wide
range of other formats. You can obtain this package by FTP from ftp.x.org
(contrib/pbmplus*.tar.Z) or ftp.ee.lbl.gov (pbmplus*.tar.Z). There is also
a newer update of this package called NETPBM, available from
wuarchive.wustl.edu under directory /graphics/graphics/packages/NetPBM/.
Unfortunately PBMPLUS/NETPBM is not nearly as portable as the IJG software
is; you are likely to have difficulty making it work on any non-Unix machine.
A different free JPEG implementation, written by the PVRG group at Stanford,
is available from havefun.stanford.edu in directory pub/jpeg. This program
is designed for research and experimentation rather than production use;
it is slower, harder to use, and less portable than the IJG code, but it
implements a larger subset of the JPEG standard. In particular, it supports
lossless JPEG.
FILE FORMAT WARS
================
Some JPEG programs produce files that are not compatible with our library.
The root of the problem is that the ISO JPEG committee failed to specify a
concrete file format. Some vendors "filled in the blanks" on their own,
creating proprietary formats that no one else could read. (For example, none
of the early commercial JPEG implementations for the Macintosh were able to
exchange compressed files.)
The file format we have adopted is called JFIF (see REFERENCES). This format
has been agreed to by a number of major commercial JPEG vendors, and it has
become the de facto standard. JFIF is a minimal or "low end" representation.
Work is also going forward to incorporate JPEG compression into the TIFF
standard, for use in "high end" applications that need to record a lot of
additional data about an image. We intend to support TIFF in the future.
We hope that these two formats will be sufficient and that other,
incompatible JPEG file formats will not proliferate.
Indeed, part of the reason for developing and releasing this free software is
to help force rapid convergence to de facto standards for JPEG file formats.
SUPPORT STANDARD, NON-PROPRIETARY FORMATS: demand JFIF or TIFF/JPEG!
TO DO
=====
In future versions, we are considering supporting progressive JPEG
compression, the upcoming JPEG Part 3 extensions, and other improvements.
As always, speeding things up is high on our priority list.
Please send bug reports, offers of help, etc. to jpeg-info@uunet.uu.net.
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