Hi, I have a problem with the distinction between colorspaces and color characteristics. I'm writing a basic transfer characteristics between lin, log, sRGB, rec601, rec709... I'm writing something like I talked for colorspaces, in the mail about "color_correct": * a specialization between each color characteristic and lin * a generic conversion to a templated type using an intermediate lin conversion I have two problems: 1) I have written a per channel functor, which seems to be the right way. But I don't know how to not apply it on the alpha channel if there is an alpha channel... without loosing performances because my common usage is rgba :). 2) I don't know how we can connect this with color_convert, because if we want to make a conversion from RGB to gray, we have to assume that RGB is linear (?) and we need to precise if we want a rec709 or rec601 luminosity... GIL code use an approximation of Rec601 to compute the luminance. Y' = 0.299 R' + 0.587 G' + 0.114 B' (Rec. 601 coefficients) Y' = 0.2126 R' + 0.7152 G' + 0.0722 B' (Rec. 709 coefficients) Best regards, Fabien