Path: utzoo!attcan!uunet!mailrus!cs.utexas.edu!usc!ucsd!ames!pacbell!osc!jgk
From: jgk@osc.COM (Joe Keane)
Newsgroups: comp.graphics
Subject: Re: RGB color mixing/averaging
Keywords: RGB, super-sampling, transparency
Message-ID: <2201@osc.COM>
Date: 16 Mar 90 23:20:15 GMT
References: <173@yak.COM>
Reply-To: jgk@osc.COM (Joe Keane)
Organization: Object Sciences Corp., Menlo Park, CA
Lines: 15

In article <173@yak.COM> tpd6908@yak.COM (Tom Dickens) writes:
>The problem I have is I expect the resulting rgb value to follow 
>'real world' results.  (ie. case1: red+blue=purple, case2: blue+yellow=green)
>Case1 works in rgb space, but case2 does not.

Averaging in RGB space does in fact average the colors, assuming you account
for gamma correction.  I think the problem is that your `real world' cases are
wrong, or at least over-simplified.  If you combine pure blue and pure yellow
light, you get washed-out green light, not pure green.  Similarly, if you mix
bright blue and bright yellow paint, you get dirty green paint, not bright
green.  Try these some time if you don't believe me.  Also, despite what some
people might say, mixing red and green light gives you only passable yellow
light, which is why you can't get a really good yellow on an RGB monitor.
Purple is sort of a special case.  It doesn't correspond to any point in the
spectrum, and you can get it exactly by mixing pure red and pure blue light.