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From: mike@hou2e.UUCP (M.LUKACS)
Newsgroups: net.physics
Subject: Re: color vision: not a fourier transform...
Message-ID: <255@hou2e.UUCP>
Date: Wed, 22-Aug-84 11:37:45 EDT
Article-I.D.: hou2e.255
Posted: Wed Aug 22 11:37:45 1984
Date-Received: Thu, 23-Aug-84 00:47:56 EDT
References: <188@mhuxm.UUCP>, <698@opus.UUCP>
Organization: Bell Labs, Holmdel NJ
Lines: 33

<........>
Although the physical basis of normal human color perception consists of
three overlaping sensitivity curves corresponding roughly to the "red",
"green", and "blue" areas of the visual spectrum, the psychophysical
color sense is much more complex and depends on a lot of post-processing,
both automatic and cognitive (relying on memory and expectation).
Early experiments by Land (the founder of Polaroid corp. originally
Polaroid-Land) showed that under some conditions of intensity and composition
most people could see a full color image projected in only two primaries.
Later experiments at Bell Labs by C.B.Rubinstein, D.E.Pearson, and myself
(~1969->1972) which removed any memory cues by using randomly generated
quilts of color patches, proved that normal human observers would perceive
near perfect renditions of color (all colors being present and identifiable)
from images projected by red and white primaries only.  The mechanism which
causes this is the adaptation of vision to the average color content of a 
scene.  This same mechanism can be seen operating when you look at a scene
under different illuminations such as flourescent and incandescent lights
or bright sun at noon vs. late afternoon sun vs. blue sky shade.
We tend to see almost the same colors in all these situations (excepting
pathologic pigments and/or lightings, which tend to have emitted or 
reflected spectrums with most of the energy concentrated in a few narrow
frequency bands), but any photographer will tell you that the senes do
not look at all similar to film or other nonadaptive media.  Modern
color television cameras have circuitry to mimic this effect of the human
visual system, the camera operator must push a button to "white balance"
the camera while looking at a portion of the scene that looks neutral
in color to the operator.

				Michael E. Lukacs   Room 2C-426
				Bell Communications Research
				Holmdel, N. J. 07733

				houxm!houxe!mike