Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!bionet!ames!eos!jbm
From: jbm@eos.UUCP (Jeffrey Mulligan)
Newsgroups: comp.graphics
Subject: Re: How to map 24-bit RGB to best EGA/VGA palette?
Keywords: RGB EGA VGA color
Message-ID: <4862@eos.UUCP>
Date: 25 Aug 89 19:05:48 GMT
References: <3129@cbnewsm.ATT.COM> <7743@cbmvax.UUCP> <13319@well.UUCP> <586@celit.com>
Distribution: na
Organization: NASA Ames Research Center, California
Lines: 33

billd@fps.com (Bill Davidson) writes:

>Speaking of dithering, I understand how to use Floyd-Steinberg for
>color.  It's quite simple since you keep an error vector in RGB
>three-space instead of just an error value.  This makes sense since
>it will pull colors back against the error in the adjacent pixels.

I have experimented with transforming the rgb error to luminance
and chromatic components, and then diffusing the error
using different spread functions for these components,
imotivated by the observation that the eye is
less sensitive to chromatic modulation than to luminance modulation.
This works fairly well, although it is hard to quantify the improvement.

>How would one do an ordered dither in color or does this even make
>sense?  It doesn't make sense to me.  Do you set up more matrices?

What I've done is just dither r, g, and b independently and then
combine them into a 3 (or more) bit image.  There are some interesting
questions regarding the choice of the three matrices.

I am working on a paper on this topic for the February SPIE meeting
(to be held in Santa Clara), so if anyone knows of any prior work
in the area I would very much like to hear about it.

jeff


-- 

	Jeff Mulligan (jbm@aurora.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 239-3, Moffet Field CA, 94035
	(415) 694-6290