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From: chidsey@smoke.brl.mil (Irving Chidsey)
Newsgroups: sci.bio
Subject: Re: Primary colors in human color vision
Message-ID: <15574@smoke.brl.mil>
Date: 25 Mar 91 14:13:36 GMT
References: <00945FE5.1F9B5480@aclcb.purdue.edu>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 47

In article <00945FE5.1F9B5480@aclcb.purdue.edu> miguel@aclcb.purdue.edu (Phillip) writes:
<
<   The additive primary hues, according to an undergrad general psychology 
<text book I have (Gleitmann (sp?)), are blue and yellow (which are 
<complementary) and red and green (complementary).  Blue, yellow and green 
<all have a "unique" wavelength at which the human eye/brain percieves them 
<to be without tinges of any other color.  Red is "extra-spectral" in that 
<it requires a combination of wavelengths to produce a "pure red" 
<sensation.  The complementary hues when mixed in equal amounts produce 
<grey (i.e. blue + yellow = grey).  The process is called "opponent-pair" or 
<something similar.  Mixing (adding) non-complementary hues produces an 
<intermediate color (i.e. red + yellow = orange).
<    The subtractive primaries are different.  Two pigments mixed together 
<only allow wavelengths neither absorbs to be reflected.  
<    So how does a color TV work?  I understand that it uses only red green 
<and blue and that red and green mixed together (and surely this would be an 
<additive process, not a subtractive one) produce yellow.
<    Does anyone know?
<                                    _            _
<Phillip SanMiguel        _/  \     /  \  Purdue University Juggling Club
<miguel@aclcb.purdue.edu (_)   \   /    |   *Juggling*Unicycling*COMBAT*

	There is something called a C.C.I.E. diagram which plots all visible
hues.  It is roughly, (very), triangular.  If you plot the locations of any
three light sources on this diagram and connect them by straight lines they
will define a triangle.  By varying the brightness of these sources, you can
produce light that appears to match any light source that maps to the inside
of the triangle.  The light sources you can mimic depend on your initial 
choice of your 'primary colors'.  You can perform a similar excersize with
one white source and any three filters or pigments.  The two sets of three
listed in the books are the optimum sets, but you don't have to use them.
	You can do a little better if you don't restrict yourself to three.
I believe some high quality printers may use up to 8 or so, the final
decision is economic, which usualy means 3, because the additional sources
or filters don't add much.  But 3 are essential.
	The reason you can do all this is the human eye.  It only has three
sets of color receptors, and their color ranges overlap.

								Irv

	Oh yes, your TV is color additive, usualy called RGB for red green
and blue.
-- 
I do not have signature authority.  I am not authorized to sign anything.
I am not authorized to commit the BRL, the DA, the DOD, or the US Government
to anything, not even by implication.  They do not tell me what their policy 
is.  They may not have one.		Irving L. Chidsey  <chidsey@brl.mil>