Re: illuminants
Re: illuminants
- Subject: Re: illuminants
- From: "Bertho Boman" <email@hidden>
- Date: Wed, 12 Nov 2003 23:20:36 -0500
----- Original Message -----
From: <email@hidden>
>
Bertho,
>
One method is to perform a spectral camera characterization to get the camera
>
spectral responses (a major undertaking).Then for each image, estimate the SPD
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of the white point for which the image was taken, then calculate the profile
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for that white point. Remember, you can only calculate an illuminant's
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spectral power distribution (SPD) from the color temperature under very narrow
>
conditions such as the D-series or blackbody where the relationship is known.
In
>
general, many different spectral power distributions can have the same
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correlated color temperature (CCT) or tristimulus values (color). This is
related to
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illuminant metamerism. So the ACR idea is sensible: Take two very different
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illuminants with different CCTs and color that span typical usage conditions.
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Determine profiles for both. Interpolate between them as intelligently as
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possible depending on the camera's estimated scene white point for each image
>
>
Eric Walowit
>
Tahoe
Thanks Eric for the detailed explanation.
The first part is what I have been thinking and trying to express. I guess that
previous comments have been that the two ACR profiles are just different color
temperatures, which could be calculated, but they are actual non-blackbody test
conditions. Do you or anyone else know what actual illuminants and/or
conditions they are taken?
TIA
Bertho
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