1998.11.18 13:50 "Re: lzw decompression.", by James Palo

Some companies early on did try to take them to court and Unisys spent a large sum to enforce the patent. There is no justice, in the legal system its who has the most money. Most companies have just paid Unisys since it was cheaper than fighting the patent. For the record the patent states:

The compression of a serial character stream for transmission.

Which should not really apply to Gif or lzw reading of images. But this is a fight you will not win win Unisys. Most companies have just not used the lzw.

Lzw is not lz the w is Welch at Unisys added using a string table when compressing. There are a large number of patents on all sorts of variants of LZ, LZW and even the zlib compression is LZ77 which is supposed to be patent free. We do need a good lossless compression, but zlib used in the PNG format is to complicated for general widespread use.

Jim Palo

Snowbound Software

Best regards
Jim Palo <palo@snowbnd.com>
Snowbound Software tel: 617 630-9495 fax 617 630-0210
website: http://www.snowbnd.com
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