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GIF compression support in ImageMagick

Yes, this is related (marginally) to IDL.

In the discussion on the lack of GIF support in IDL 5.4 a month or two ago,
I said that ImageMagick (http://www.imagemagick.org/) was a good tool for
creating GIFs. Although I have used ImageMagick for years I don't create
GIFs very often. And I failed to notice that some time recently the
following comment has appeared in the README:


--enable-lzw (configuration switch)

Unisys reportedly claims a patent on the algorithm supporting LZW
compression (e.g. used by GIF and TIFF). To avoid possibly infringing on
this patent, support for LZW is disabled by default. With LZW support, GIF
files written by ImageMagick will be much larger than expected


This explains the enormous increase in size when I converted some files from
PNG to GIF the other day!

So ImageMagick is not a good tool for creating GIFs (unless you go to some
trouble to enable LZW compression) and IDL is not the only organisation
abandoning GIF because of patent issues.

All the more reason to BURN ALL GIFS, I say.

BTW, ImageMagick can still *read* compressed GIFs.

Mark Hadfield
m.hadfield@niwa.cri.nz  http://katipo.niwa.cri.nz/~hadfield
National Institute for Water and Atmospheric Research