Archive of UserLand's first discussion group, started October 5, 1998.

Re: LibGd and LZW

Author:Eric Kidd
Posted:8/29/1999; 3:07:10 PM
Topic:GIFs get expensive
Msg #:10207 (In response to 10205)
Prev/Next:10206 / 10209

(I'm speaking for myself, not for UserLand.)

If PNG was signifigantly better than GIF, I might feel better about taking the plunge and breaking compatibility with the ubiquitous GIF format, but its only virtue seems to be that it's not LZW.

PNG offers better compression, more than 256 colors, and a real alpha channel (not just a single transparent "color"). It is unpatented and reference code is available. It does not, however, support animation. Overall, PNG is a better format than GIF, but it's not as widely supported.

Unfortunately, browser support for PNG is marginal. Everybody has known about the Unisys patent since before Netscape 1.0, and the browser vendors have just started to implement alternatives.

That's why option 2, RLE GIF files, seems so satisfying. If word comes back from the patent lawyers that it's safe to use without paying Unisys, I would love to use it.

The Unisys LZW patent does not (by any sane standard) have anything to do with run length encoding. Other RLE-related patents do exist, and may or may not be relevant. Of course, I'm not qualified to give you legal advice on this subject. :-)


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