stpeters@dawn.UUCP (11/12/88)
>This follows Dick St Peters' comment in <8811080030.AA14681@EXPO.LCS.MIT.EDU> >of Comp.windows.x that (R+G+B)/3 is an appropriate weighting >function for luminance. I didn't say any such thing; I said that (R+G+B)/3 is an appropriate weighting for *white*. In fact, the basic point of my article is that luminance and whiteness are not equivalent. >Sorry to air the laundry in public. Fabric whiteners work by adding >materials which flouresce to convert ultraviolet light [to which the human >eye is not sensitive] into visible light in the blue part of the spectrum >[to which it is]. The shirt not only looks brighter than white, it IS >brighter than white. But this has nothing to do with the luminance >coefficients. Agreed. It has nothing to do with luminance coefficients. It has a lot to do with subjective "whiteness". Adding more blue to make the white brighter than the CIE/NTSC TV white point makes a human perceive the shirt as whiter. Just like I said originally. Thank you. >To achieve accurate colour reproduction requires specification of >reference white. This is a lurking problem for accurate colour >reproduction in computer graphics, because most workstation monitors are >adjusted for a white point (of about 9300 K) that's quite a bit more blue >than the television standard. It's a lurking benefit, not a lurking problem, *unless* you're going to try to use the workstation monitor to display (NTSC) color TV. The television standard has no relevance for contexts that do not require an intermediate tranformation into coordinates with a luma axis orthogonal to a chroma plane. Mr. Poynton and I are in agreement on one very important point: color is a far more complex topic than meets the eye (sorry - I couldn't stop my fingers in time). -- Dick St.Peters GE Corporate R&D, Schenectady, NY stpeters@ge-crd.arpa uunet!steinmetz!stpeters