data compression link collection

GIF - Compuserve's Graphics Interchange Format

In the late 80s Compuserve was the dominant Online Information Service. As such, they created a standard for graphics files called the Graphics Interchange Format, or GIF. Because of their influence, the GIF file format soon became very popular. When the first WWW browsers supported GIF fiels, the format became even more popular. GIF is documented here because it relies on LZW compression is used to store image data internally. This became an important fact after Unisys decided to start imposing patent royalties on developers who created programs that created or displayed GIF files

Scilab Image Processing Toolbox

SIP intends to do imaging tasks such as filtering, blurring, edge detection, thresholding, histogram manipulation, segmentation, mathematical morphology, color image processing, etc.
These operations are useful for problem solving in real-world applications ranging from car motion planning to automatic diagnosis of medical images.

Version 0.3.1 is shipping as of May, 2004.


Posted in May 2nd, 2004

Working with GIF images in Delphi

A straightforward article with some discussion and links.


Posted in April 11th, 2004

Replacing a Dictionary with a Square Root

Tom Cagill creates GIF files without using LZW.


Posted in March 14th, 2004

Libungif - An uncompressed GIF library

A library for reading and writing gif images. The save functionality uses an uncompressed gif algorithm to avoid the Unisys LZW patent. This library is based on Eric Raymond’s giflib and implements a superset of that library’s API.

Version 4.1.2 of this library shipped in March, 2004.


Posted in March 7th, 2004

GIF Construction Set Pro

GIF Construction Set Pro represents the state of the art in GIF animation software. It will assemble your original animations effortlessly through its Animation Wizard, squeeze them down to as close to nothing as possible with its Supercompressor; create eyecatching banners and animated transitions; manage your GIF files; add transparency to existing graphics and a lot more.

Version 2.0.44 is shipping as of February, 2004.


Posted in February 8th, 2004

(X)MedCon - Medical Image Conversion Utility

A free program to deal with image formats in popular medical formats, including DICOM, SPM, PNG, and GIF.

Version 0.9.1 of (X)MedCon shipped in January, 2004.

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Posted in January 11th, 2004

Advanced GIF Optimizer

This program is designed to help you squeeze the maximium amount of space out of GIF files while keeping the image quality at an acceptable level. Commercial code, but a free download is available.

Version 4.0 is shipping as of December, 2003.


Posted in December 2nd, 2003

Arcsoft Mobile Media Codecs

Arcsoft has a line of mobile media codecs that includes support for MIDI, JPEG, PNG, GIF, and speech.


Posted in October 29th, 2003

License Information on GIF and Other LZW-based Technologies

A Unisys press release explaining their beliefs regarding licensing required to use GIF technology in your products. As of this posting (8/2003) the US patents appear to have expired, but there are European and Japanese patents will not expire until some time in 2004.

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Posted in August 24th, 2003


Convert your GIF files to PNG format under UNIX, Linux, or Win32.


Posted in August 1st, 2003

Trout’s GIF Optimizer

This freeware program is designed to help you reduce the size of your GIF files. There are certain optimizations that can be performed with absolutely no loss of quality, as well as some that can provide additional improvements with some loss of resolution. Best of all, Trout’s GIF Optimizer is completely free.

An anonymous reader complained They call it freeware then make you pay. To be honest, I can’t see any indication of this on the web site, other than the usual request for donations. Somebody correct me if I’m wrong!


Posted in May 17th, 2003


Corona is an image input/output library that can read, write, and manipulate image files in just a few lines of code. It can write PNG files, and read PNG, JPEG, PCX, BMP, TGA, and GIF. Corona was designed to be easy to use, and exports a straightforward C++ API. With just a few lines of C++, you can add image loading to your application.

Corona 1.0.1 shipped in May, 2003, and added support for TGA images as well as a few more functions.

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Posted in May 17th, 2003

Real GIF Optimizer

A GIF optimizer seeks to reduce the size of your GIF files, usually without compromising image quality. Not enough detail on this site to pass judgment, but good GIF optimizers will also let you reduce the number of colors in the palette dynamically, so you can see the effect.

Real GIF Optimizer 3.05 shipped in February of 2003. I wish I could tell you what new features are in this release, but RealMultiMedia Development is one of those companies that doesn’t bother to post release notes on their web site!


Posted in April 3rd, 2003

zlib and libpng for Windows CE

Kazuo Adachi ported both of these important packages to Windows CE and Windows CE .Net. This includes binaries for what I believe are all the currently support CPUs.


Posted in March 31st, 2003

Compressed Image File Formats: JPEG, PNG, GIF, XBM, BMP by John Miano

“Compressed Image File Formats is an appealingly compact and useful guide to some of today’s most popular file formats used for image data. For any programmer who needs to know how images are stored, this concise reference can serve as a really invaluable resource.”
Note that the source code for this book includes an independent implementation of a PNG codec, which may be one of a kind. Link to the source code on this page.

Please use
this link to purchase the book through Your purchase will help support this web site.

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Posted in March 21st, 2003

Ultra GIF Optimizer

Ultra GIF Optimizer is a powerful tool for optimizing GIF images. It can makes your web page load faster,save your server bandwidth charges and disk space! This is a commercial product, but it looks like you can download it and have a trial session.


Posted in September 22nd, 2002

LZW and GIF explained

A guy named Steve Blackstock takes a shot at making this all clear to you. Gives some details on the LZW variation used in GIF files.


Posted in June 4th, 2002

Web Graphics

A tutorial page discussing the various image formats currently in use on the web. Nice comparisons and a good set of links.


Posted in April 17th, 2002

True-Color GIF Example

Yes, it is possible to create GIF images with far more than 256 colors. This page will show you exactly how that is done, or at least prove to you that it is possible. It links to a GIF library called ANGIF that purports to be able to pull this trick off.

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Posted in March 19th, 2002

Wikipedia Entry: GIF

The Wikipedia entry for GIF. A reasonable amount of background and overview information.


Posted in January 27th, 2002

GIF89a Animation Browser Test

These pages will test the various features available for GIF89a animation. Each feature is tested as independently as possible, allowing you to identify what features your browser supports and how well. The pages isolate features to prevent combination collisions (one error causing another feature to fail). Each test is composed of an animation that tests the most basic quality of the function.


Posted in December 7th, 2001

GIF87A Specification

This is a copy of the original GIF specification from CompuServe. It was expanded significantly by the 1989 specification.


Posted in December 7th, 2001

GIF89A Specification

Another copy.

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Posted in December 7th, 2001

Additional GIF format documentation

Royal Frazier’s All About GIF89a, a bountiful page of documentation on the file format.


Posted in December 7th, 2001

Add GIF-animation to your MFC and ATL projects

Decoding GIF files and displaying them without help isn’t particularly easy. Add animation to the task and you’re looking at a ton of work. Fortunately, this MFC-compatible set of classes on the CodeProject web site does the heavy lifting for you.


Posted in October 8th, 2001

Compression, Encoding and Graphics Files - A Practical Tutorial

Tutorial by Rich Holowczak from Rutgers U. A set of slides that would probably be really useful if you had the lecture to go with it. Without the lecture, not so hot.


Posted in November 17th, 2000

The GIF Controversy: A Software Developer’s Perspective

Some thoughts by a person only known as mcb on the GIF patent controversy.


Posted in January 1st, 2000


InterGIF is a freeware program for making animated GIFs. It claims to do a good job of optimization. I have feedback from one use who was quite happy with the results - a sample GIF created by GIMP was reduced from 2235 bytes to 1455. Not bad.

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Posted in November 21st, 1999

Lzw, gif decoding

Arturo Campos describes the specific implementation of LZW compression used in GIF files.

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Posted in November 17th, 1999

GIF89A Specification

This is a copy of the second GIF specification from CompuServe. It added quite a few features to the GIF format. Probably the best well known of these would be the ability to add animation to GIF files.

Reader Andrew T. says: The definitive document, what more can you ask for?


Posted in September 21st, 1999