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From: todd@uhccux.UUCP
Newsgroups: sci.physics,comp.graphics,comp.sys.ibm.pc
Subject: Re: Color questions: color systems, "black bodies", EGB palette
Message-ID: <520@uhccux.UUCP>
Date: Fri, 29-May-87 04:23:22 EDT
Article-I.D.: uhccux.520
Posted: Fri May 29 04:23:22 1987
Date-Received: Sat, 30-May-87 08:37:19 EDT
References: <1937@druhi.ATT.COM> <725@bsu-cs.UUCP>
Reply-To: todd@uhccux.UUCP (The Perplexed Wiz)
Distribution: comp
Organization: U. of Hawaii, Manoa (Honolulu)
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Xref: utgpu sci.physics:1406 comp.graphics:651 comp.sys.ibm.pc:3865

In article <725@bsu-cs.UUCP> dhesi@bsu-cs.UUCP (Rahul Dhesi) writes:
>This problem of terminology comes up again and again.  People, the human eye 
>needs only three distinct hues for full effect.  This business of 8 colors, or 
>64 colors, or 4096 colors, is advertising hype.  Your typical printer will 
>tell you he or she uses only three colors, with a little black thrown in.  The 
>rest is all a question of INTENSITY.

You are wrong.  Just some of the things color perceptions depends on are:

	1. whether the human eye(s) are "normal" for color vision
	   (i.e., the person is not "color-blind")
	2. the other colors and shadows surrounding the color surface or
	   source (in the case of lights)
	3. the mixture of wavelengths reaching the eye.
	   Subtractive mixture takes place in paints (where Red, Yellow,
	   and Blue are the "primaries").  Additive mixture takes place
	   when using lights (where Red, Green, and Blue are the "primaries")
	4. the amount of light reaching the eye
	5. the current state of the visual system.  If you are dark adapted
	   and are suddenly flooded with light, all you see is a white
	   glare most of the time.  If your opponent cells are fatigued
	   in one direction the complentary color (of whatever is fatigued)
	   is seen (try placing a green lens over one eye for a few mintues
	   and then look around).

In short, the color you see depends not only on the actual wavelengths
reaching your eye, but also interaction of color after being processed
by higher cortical functions, and the current state of various portions
of the visual system.  Further, the while only three "primaries" are needed
to create all the colors we "see," the "normal" human eye is capable
of distinguishing a great many "colors" (some estimates approach or
exceed one billion).  Anyone who wants to find out more about the
processing of color by the human visual system should read a good book
on the subject.  I think Robert Boynton's "Human Color Vision" may be
a good place to start....todd

-- 
Todd Ogasawara, U. of Hawaii Computing Center
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