Thank you, Mukund, ... On Tue, Oct 21, 2014 at 10:47 AM, Mukund Sivaraman <muks@xxxxxxxx> wrote: > Hi Robert > > On Tue, Oct 21, 2014 at 10:04:14AM -0500, Robert Hanson wrote: > > http://chemapps.stolaf.edu/jmol/test/dither.htm . The solution was to > > This page seems to use JavaScript and WebGL, and so I'm not able to view > it. It would have been better if you had sent a link to static images of > the source and result. > It's not WebGL -- just HTML5. But that is a fine idea: http://chemapps.stolaf.edu/jmol/test/dither2.htm > > > 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. > > So you are doing FS dithering with a fixed uniform palette? > That sounds right. I'm not familiar with the lingo here. Equal partitions along R G B coordinates. > > > 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. > > You are looking for color quantization methods. You can find description > of an octree method in Graphics Gems I. GIMP uses median cut. > > See https://www.cs.cmu.edu/~ph/ciq_thesis for Heckbert's thesis on > median cut. > > That's helpful. So we have n colors, each with p_i pixels. This median cut idea just considers the n colors, not p_i, correct? (Ignores frequency?) How is this then also implemented with Floyd-Steinberg dithering? Is the idea that the averages of the median cut boxes form our fixed points for the dithering? That a nearest-point calculation is done to generate the error function? Can you point me to the place in the GIMP code this is accomplished? Bob -- 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 _______________________________________________ gimp-developer-list mailing list List address: gimp-developer-list@xxxxxxxxx List membership: https://mail.gnome.org/mailman/listinfo/gimp-developer-list List archives: https://mail.gnome.org/archives/gimp-developer-list
