P3D Color temperature

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

C.S. McCamy's approximation for correlated color temperature for use between
2000K and 10000K is CCT = 437 n^3 + 3601 n^2 + 6831 n + 5517, where
n = (x - 0.3320) / (0.1858 - y), and x and y are from the 1931 CIE
color coordinates. It is noted in other references that the concept of color
temperature is essentially meaningless except when the color in question is
near the Planckian locus (the curve made up of black body color points).

In other words, the concept of color temperature is highly unproductive
for many of the things 3D photographers would be interested in, and misuse of
the concept causes harm by spreading misinformation. Color essentially
requires two parameters (i.e. (x,y), or (u',v') for accurate description, 
and color temperature attempts to describe it in one parameter. It's like
trying to describe how to travel from one location to another by giving the
distance but not the direction.

These color descriptions are relevant to how a *human* would perceive a color -
they are probably not sufficient to describe the response of film or video
camera.

John R


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