Data Compression


Criteria

Survey Formats

Basics

Compression Methods

Data Formats

Files

Audio Data

Image Data

GIF

Colours

Data Compression

Characteristics

GIF87a

GIF89a

Patents

Optimizations

Examples

Drawings

JPEG

Video Data


Glossary

Index


Download


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GIF - Patents


The central mechanism for the compression of the picture contents is based on the LZW procedure as developed by Terry Welch. Sperry, his employer at that time, patented the algorithm in 1983 (US-Patent: 4,558,302).


Later on, Sperry was bought by Unisys, which started in the early 90s to use the patent commercially. Since then licenses are necessary to utilise GIF. A large number of freeware, shareware and open source projects does not support the GIF format for that reason.


As far as known, the patent valid for the United States expired in 2003. There are further patents of the same contents having their validity to 2004 at least in Germany and Japan.


Whether the format can be used afterwards freely, is not finally cleared also after the expiration of the two national patents. On the one hand further patents may exist in other regions and on the other hand questions regarding the protection of GIF as a product are still discussed.


GIF is not the only graphic format, which is affected by this patent. TIFF and Postscript use also LZW for lossless data compression. The software producers also paid appropriate royalties. At least with TIFF files frequently incompatibility problems appear because only a part of the applications supported LZW compression.


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GIF - Graphic Interchange Format GIF89a GIF - Optimizations