Chromatic adaptation -- original Von Kries ideas
Chromatic adaptation -- original Von Kries ideas
- Subject: Chromatic adaptation -- original Von Kries ideas
- From: Allen Furbeck <email@hidden>
- Date: Thu, 2 Jul 2009 21:29:49 -0400
I would think that chromatic adaptation and color constancy are
clearly related. There was a BBC Horizon TV show on color constancy
some years back worth finding if one can, entitled "Colorful Notions".
Edwin Land did some testing and came to the conclusion that the brain
is scanning the scene (much like auto white balance I would think) and
creating a white balance from the relationships between colors. He
called his test patches "Mondrians," although the only thing they
really had in common with the paintings is rectangularity.
An effect of this is that if a colored light is used to cast a shadow
of a on a wall the shadow will be black, but if there is enough white
light present to fill in the shadow then it will appear to be colored
the compliment of the colored light. The cool part is that by
photographing a scene through the proper gels (I'm sorry, but I'm not
100% sure on the details) you can then re-project the images one with
red light and one with white light and get a remarkably more complete
version of full color than you would ever imagine.
In truth I'm a bit confused as to how much of this is in the Horizon
show and how much was in an episode ("Island of the Color Blind") of a
later show ("The Mind Traveller") that was based on Oliver Sacks
writings, as I saw both shows at about the same tme and they are a bit
mixed up in my mind. Sorry. They're both quite interesting though.
Roger wrote
Message: 2
Date: Tue, 30 Jun 2009 19:10:18 -0400
From: Roger <email@hidden>
Subject: Chromatic adaptation -- original Von Kries ideas
To: 'colorsync-users List' <email@hidden>
Message-ID: <003c01c9f9d7$ef83ffe0$ce8bffa0$@ca>
Content-Type: text/plain; charset=US-ASCII
Hello folks,
I've been digging into the original concepts behind chromatic adaptation
lately and found myself returning to the Von Kries literature. His
rules of
adaptation state that the cones spectral sensitivities are invariant
(fixed)
and independent from each other. Chromatic adaptation is often
presented in
the context of how to adapt some object color tristimulus values
between two
sets of illumination or illuminants (D50 vs D65 as in ICC PCS). But I
also
often find mention of this idea of 'Reference', as in Reference white. I
realize that the Reference white in question is the one to which the
observer is currently adapted. But could there be another notion of
Reference White where our that our brain has always access to? To
which all
illuminations are always compared? Naturally? Possibly linked to the
idea of
color constancy?
I don't find anything in the literature to substantiate this idea. Is
this
too far-fetch an idea or could this make any sense conceptually? For
example, suppose I observe a red apple under direct sunlight. My brain
has
no problem recognizing the apple from the combined apple spectral
reflectance and sunlight spectral energy. My cones, somehow, are
adapted to
this "sunlight" and correctly infer the visual cues from the scene to
adjust
the Von Kries Coefficients in my cones, so to speak, so that the red
apple
appears like a red color I've learned to expect.
But suppose I now step indoor with my red apple, and I'm seeing it under
tungsten light. My question is : could it be argued that the "red" color
will appear red as though my brain has somehow adjust the gain
sensitivities
of my cones to render the red to some abstract, possibly innate,
notion of
"white", that would be independent of the scene? Maybe I'm trying to
read
too much in chromatic adaptation?
Roger
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