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

[Robert Hanson <hansonr stolaf edu>]

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
http://www.stolaf.edu/people/hansonr


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