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From: chassin@rpics.UUCP
Newsgroups: comp.graphics
Subject: Re: Colour vision
Message-ID: <979@rpics.RPI.EDU>
Date: Thu, 12-Mar-87 13:30:22 EST
Article-I.D.: rpics.979
Posted: Thu Mar 12 13:30:22 1987
Date-Received: Fri, 13-Mar-87 23:48:20 EST
References: <505@ubu.warwick.UUCP>
Lines: 54
Summary: Color is in the eye of the beholder...

In article <505@ubu.warwick.UUCP>, rolf@warwick.UUCP (Rolf Howarth) writes:
> 
> With the recent discussion about how to map colour images to black-and-white,
> I thought I'd ask if anyone could explain to me how the human brain
> perceives colour.
> 
> One thing that always puzzled me at school was being told, for example, that
> red + green light "gives you yellow", where "yellow" is also what you see
> at a particular position in the spectrum (when you shine white light
> through a prism). As far as I understand it, these two "yellows" are different
> spectroscopically , yet the eye perceives them to be the same colour.
> I think I was confused because the distinction between what a colour *is*
> and how it *appears* to the eye was never made very clear.
> 

I not very expert on physiology but as far as I understand it color is an 
interaction between a mass of photons, the cones in the retina, and the
coding sent to the brain. There are I believe two types of color sensing cells
in the retina: red-green and yellow-blue. I don't know how the cones send
their info to the brain via the optic nerve. I was told however the the cones
react only to their type of light. A red-green will swing to the red side in
response to a red low frequency photon and swing over to the green side as
the photons get more energetic (greener color). A yellow blue does the same
thing but at a higher frequencies. There is an overlap which I believe accounts
for the strongly favored green region. This makes sense since this is the
peak output frequency of the sun. I also was told that the response curve
actually matches the radiation emission curve for the temperature of the
sun.

Sorry I can't give you sources, or more detail, I don't know much more...

I'm sure other people will be able to give more detail and/or likely
corrections.

I do want to comment that this is an interesting subject to me in terms
of human perception, and video displays. Their is no doubt in my mind that
a video display offers an incomplete picture, so to speak. To be more complete
a display would have to either be capable of generating all frequency photons
rather than three specific. The other option would be to generate to ranges of
light that can affect the retina in a way equivalent to the way 'natural' light
does. Either of the ways would be transparent, giving the real colors.

_____________________

David P. Chassin
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