Path: utzoo!attcan!lsuc!becker!bdb
From: bdb@becker.UUCP (Bruce Becker)
Newsgroups: comp.graphics
Subject: Re: RGB color mixing/averaging
Keywords: RGB, super-sampling, transparency
Message-ID: <6020@becker.UUCP>
Date: 15 Mar 90 09:59:35 GMT
References: <173@yak.COM>
Reply-To: bdb@becker.UUCP (Bruce Becker)
Organization: G. T. S., Toronto, Ontario
Lines: 43

In article <173@yak.COM> tpd6908@yak.COM (Tom Dickens) writes:
|I am looking for a simple routine that will take 2 rgb values, a ratio
|for mixing them (ie. 0.5), and will return the resulting rgb value.
|This is desired for determining a pixel color after super-sampling, or when
|combining colors while working with transparent surfaces.
|
|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.  I have read multiple
|articles on the subject and have experimented with converting to HSV,
|CMY, HLS spaces, linearly mixing, then converting back, but have not
|gotten satisfactory results.  I have an appreaciation for the physical
|aspects of light and properties of different materials etc., but what I
|need is a quick and simple method that works as expected.  I am in the
|process of deriving such a method since I have not found any papers
|which address this.  

	You need to convert to CIE coordinates in order
	to do this properly. In this color coordinate
	space color mixing occurs along a straight line
	between the given colors - this is not true of
	HLS, HSV, CMY, RGB, etc. Probably you ought to
	convert from rgb to CIE at the beginning and
	work in this form all the way through. Besides
	the efficiency gain, you end up with values
	that are independent of the color characteristics
	of any given display device or class of devices.

	Some references in which to look for more info
	and code are:

	Raster Graphics Handbook, 2nd Ed., Conrac Corporation,
	Van Nostrand Reinhold, 1985

	Illumination and Color in Computer Generated Imagery,
	Roy Hall, Springer-Verlag, 1989

Cheers,
-- 
  (__)	 Bruce Becker	Toronto, Ontario
w \@@/	 Internet: bdb@becker.UUCP, bruce@gpu.utcs.toronto.edu
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_/  \_	 "So far from God, so close to the United States" - Old Mexican proverb