install.doc | How to con |
|
| IJG software. |
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usage.doc | Usage instructions for | cjpeg, |
| djpeg, jpegtran, rdjpgcom, and | |
| wrjpgcom. |
|
*.1 | ||
| programs (same info as usage. | |
| doc). |
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wizard.doc | Advanced usage instructions for | |
| JPEG wizards only. |
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change.log |
| change |
| highlights. |
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Programmer and internal documentation: |
| |
libjpeg.doc | How to use the JPEG library in | |
| your own programs. |
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example.c | Sample code for calling the | |
| JPEG library. |
|
structure.doc | Overview of the JPEG library’s | |
| internal structure. |
|
Road map of IJG |
| |
coderules.doc | Coding style rules | |
| if you contribute code. |
|
Please read at least the
Useful information can also be found in the JPEG FAQ (Frequently Asked Questions) article. See ARCHIVE LOCATIONS below to AQ
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
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
This software implements JPEG baseline, extended- sequential, and progressive
compression processes. Provision is made for supporting all variants of these
processes, although some uncommon parameter settings aren’t implemented yet.
For legal reasons, we are not distributing code for the
variants of JPEG; see LEGAL ISSUES. We have made no provision for supporting
the hierarchical or lossless processes de standard.
We provide a set of library routines for reading and writing JPEG image
and “djpeg”, which use the library to perform conversion between JPEG and some other popular image formats.
The library is intended to be reused in other applications. In order to support
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
can be compiled out of the library if not required for a particular application. We have also included “jpegtran”, a utility for lossless transcoding between different JPEG processes, and “rdjpgcom” and “wrjpgcom”, two simple applications for inserting and extracting textual comments in JFIF
The emphasis in designing this software has been on achieving portability and , while also making it
fast enough to be useful. In particular, the software is not intended to be read as a tutorial on JPEG. (See the REFERENCES section for introductory material.) Rather, it is intended to be reliable, portable,
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
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
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)
All Rights Reserved except as speci.
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
with this copyright and
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 unmodi.
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 speci
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 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 Unix con
with GNU Autoconf.
It is copyright by the Free Software Foundation but is freely distributable.
The same holds for its supporting scripts (con. guess, con.sub, ltcon, ltmain.sh). Another support script,
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.
The IJG distribution formerly included code to read and write GIF
To avoid entanglement with the Unisys LZW patent, GIF reading support has been removed altogether, and the GIF writer has been simpli
GIFs”. This technique does not use the LZW algorithm; the resulting GIF
all standard GIF decoders. We are required to state that
“The Graphics Interchange Format(c) is the Copyright property of CompuServe Incorporated. GIF(sm) is a Service Mark property of CompuServe Incorporated.”
REFERENCES
We 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.
(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 allace’s
article is available at ftp://ftp.uu.net/graphics/jpeg/ wallace.ps.gz. The
that appeared in IEEE Trans. Consumer Electronics) omits the sample images that appeared in CACM, but it includes corrections and some added material. Note: the Wallace article is copyright ACM and IEEE, and it may not be used for commercial purposes.
A somewhat less technical, more leisurely introduction to JPEG can be found in “The Data Compression Book” by Mark Nelson and
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
The book includes the complete text of the ISO JPEG standards (DIS
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 or ITU. (Unless you feel a need to own a certi, we
recommend buying the Pennebaker and Mitchell book instead; it’s much cheaper and includes a great deal of useful explanatory material.)
In the USA, copies of the standard may be ordered from ANSI Sales at (212)
covers compliance testing methods. Part 1 is titled “Digital Compression and Coding of
Some extensions to the original JPEG standard are de
in JPEG Part 3, a newer ISO standard numbered ISO/IEC IS
The JPEG standard does not specify all details of an interchangeable or the omitted details we
follow the “JFIF” conventions, revision 1.02. A copy of the JFIF spec is available from:
Literature Department
phone (408)
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