I hope you don't mind; I reordered parts of your email when responding to it. >> Isn't the second (adapted) transform going to give us a D50 Y instead >> of a D65 Y? > > Yes, it will, and that's precisely what you want if you want to > correctly calculate an sRGB image's Luminance values from its RGB > values. The main usage for this transform (D65 RGB -> D65 Y, with the unadapted values) is to convert color images to grayscale. It seems to me that having a D65 grayscale image is correct, especially because when converting back to RGB D65 we simply copy the Y value into each of the components. I haven't really looked at the other cases of the values you pointed out yet, but none of those are widely used code paths. They should probably be examined individually. > D50 has two uses in an ICC profile: the profile illuminant and also > the profile white point for profiles with D50 white points. I don't think we should be accounting for the illuminant when converting to grayscale. > As an aside, you can't assume that any of today's LCD monitors are > calibrated to match sRGB or even to have a D65 white point Every monitor is different. D65 with the sRGB primaries is the same as ITU‐R BT.709‐5 (HDTV), which I think is a reasonable approximation for certain calculations. Nobody is claiming that our conversions are exact for an profileless, uncalibrated monitor. > So is there some > other place in the babl/gegl/gimp code where there is an actual > hard-coded matrix transform between two D65 color spaces? If so, which > two D65 color spaces? The YCbCr transform in babl might be wrong (assumes D65, in a case where we don't want D65), but you already pointed that out, and I wasn't really talking about that conversion. > Well, what I really want babl/gegl/gimp to do is stop using sRGB as > the "one space to rule them all" and instead, if there has to be a > single internal color space, make it the D50 Identity color space ... I think the main reason for choosing an sRGB-like space is because of convenience. Many images are in sRGB, and it's nice to be able to store them in 8-bits/channel without severe quality loss. People using other color spaces are more likely to use high bitdepths, where the profile choice is less critical for image quality. _______________________________________________ gimp-developer-list mailing list List address: gimp-developer-list@xxxxxxxxx List membership: https://mail.gnome.org/mailman/listinfo/gimp-developer-list
