Originally Posted by TomHuffman
CIE u'v' is just a useful convention we can use to describe the CIELUV color space minus the luminance component.
I believe this is the root of most of the misunderstanding.
CIE u'v' is a coordinate system where every chromaticity has a fixed value, d65 = 0.1978, 0.4683 u',v'
CIE L*U*V* is based on a white point, so the reference point for white is 0,0.
But if the white point is D50, the u'v' coordinates shift to 0.2092,0.4881, while L*U*V* is still 0,0 since it's coordinate system is in reference to white.
One is a competitor to L*a*b*, where you actually get perceptual saturation effects, and u'v' is the replacement for x,y where you are simply describing chromaticity without respect to perceptual saturation.
The saturation of colors based on luminance is very significant as well.
For Red the u'v' targets are always 0.4507, 0.5229
In L*U*V* at 100% they are 53.2, 175.01, 37.75
at 30% they are 12.7, 41.85, 9.02
So as drop in target luminance the ability to perceive saturation drops as wellEdited by sotti - 8/19/12 at 6:18pm