18-bit with dithering

[hatfieej]

I'm looking to convert an image to 18-bit color (6 bits for R, G, and B each) but would like it to also dither the image so the banding doesn't look as bad. I'd prefer the dithering to not be the basic ordered pattern -- something more like Floyd-Steinberg or one of the others. I've gotten the image to convert to 18-bit (using posterize and threshold), but those create banding in the image. I can't figure out how to do that with a nice dithering algorithm too. I'm sure they has to be a way, I just haven't figured it out yet. Any ideas? Thanks.

[snibgo]

If I recall correctly, "-posterize" can't dither. But you can use that to get the list of colors, then "-remap" the image to itself, or a "unique-colors" version of itself. "-remap" can dither.

It's a slightly crazy way of doing it, especially if you have many or large images. You could skip the posterize and go straight to remap by creating your own map with (2^6)^3 = 262144 entries (pixels).