RE: chromatic adaptation
RE: chromatic adaptation
- Subject: RE: chromatic adaptation
- From: "Fred Bunting" <email@hidden>
- Date: Thu, 21 Jun 2001 16:26:22 -0700
- Thread-topic: chromatic adaptation
Samer Mady wrote:
>
the eye has three kinds of color receptors. one that is most
>
sentsetive to
>
short wavelength, on that is most sentsetive to middle
>
wavelength and one
>
that is most sensetive to long wavelength. the sensitivity of
>
each receptor
>
changes according to the colour of the illumination. if the
>
illumination is
>
reddish the sensitivity of the receptors that are sensitive for long
>
wavelength will be reduced and if the illumination is blue
>
the receptors
>
that are sensitive for short wavelength will be less sensitive.
>
=> we will not be able to perceive the warmth or coolness of
>
the colour.
While your conclusion is correct, I'm not sure I agree with your
explanation of the mechanics of chromatic adaptation.
The sensitivity of the individual cones does *not* change with changes
in the color of the illumination.
Instead, what happens involves something called 'center-surround
fields.' In the visual cortex (back of the brain) are neurons that
receive signals from the retina. Each of these neurons receive signals
from a 'field' of cones. The neuron can interpret the signals coming
from cones in the center of the field differently depending on the
signals from the surrounding cones. So if the illumination is bluer,
the neurons will compensate in the way they interpret blue signals
coming from the center of the field. This is what we believe to be the
neural basis of 'color constancy.'
This is a vast oversimplification ... but that's the rough idea.
(Apologies to David Hubel, who got a Nobel prize (with Torsten Weisel)
for his work in neurophysiology, and is the only Nobel Laureate I've
actually met.)
Fred Bunting