[Gimp-developer] Floyd-Steinberg/GIF color optimization

My name is Bob Hanson; I'm the principal developer of Jmol.

Jmol can export images in a variety of ways including GIF and animated GIF.
But of course GIF only allows 256 colors, and I used to think that was the
end of that. Forget that. But then one of our users pointed me to how well
GIMP creates GIF images using the Floyd-Steinberg dithering algorithm, so I
decided to give that a try. And I was delighted with the results. (Had some
fun just playing with that -- see my 216-color solution at
http://chemapps.stolaf.edu/jmol/test/dither.htm .  The solution was to
partition red, green, and blue channels into a 6 x 6 x 6 color space,
allowing 216 colors in total. Not perfect, but amazingly good, I think.

The problem comes when I have a small molecule with not too many colors. If
I go just over 256, then the FS algorithm cuts this down to something like
64 colors. I'm wondering if I could get some advise as to how to optimize a
set of colors down to 255 colors without undershooting in such a dramatic
way while still using FS.

Bob Hanson

Robert M. Hanson
Larson-Anderson Professor of Chemistry
Chair, Department of Chemistry
St. Olaf College
Northfield, MN

If nature does not answer first what we want,
it is better to take what answer we get.

-- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900

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