|TIFF and LibTiff Mailing List Archive|
LibTiff Mailing List
2006.12.06 22:19 "Re: Grayscale, or is it?", by Graeme Gill
Joris wrote: > > If you colour model goes as far as to be based on actual physical > properties of light, it's extremely complicated to convert RGB to > "greyscale". You'll have to dig into spectra and whatnot, for all I > know. I can't agree with you on this. Taking the weighted sum of an RGB output in linear light is not an approximation, it's actually correct, equivalent to CIE Y value if the right weightings are used. The weightings simply depend on the primary locations and the white point. This is because any additive space is a 3x3 transform from CIE XYZ space, so it only takes one row of the inverse matrix to compute Y again. See <http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html> Graeme Gill.