On Mon, Jun 15, 2015 at 2:29 PM, <thomas.manni@xxxxxxx> wrote: > in master branch, using Colors > Desaturate (luminosity) and Image > Mode > Grayscale on a RGB image (whatever the image precision) gives different results. > > This does not appear in branch gimp-2-8, since the 2 actions are computed the same way (using GIMP_RGB_LUMINANCE). > > In master, for Desaturate (luminosity) filter, GIMP_RGB_LUMINANCE is used on a R'G'B'A buffer. > For Grayscale conversion, drawables' buffers formats are converted to babl_format Y (or Y' according to the initial format). > > As these 2 actions seem to have the same goal (obtain the relative luminance), shouldn't we obtain the same result ? I am not sure they should behave the same way / give the same result - nor that any of the results are ideal yet. What is GIMP_RGB_LUMINANCE? is it the equivalent of the V component of HSV (MAX(MAX(R,G),MAX(G,B)) ? It is possible that GIMP could ask the user how they want to derive a grayscale/desaturated version. Perhaps only ask when doing desaturate and do the best we can do for the implicit conversion when going from color to grayscale mode - something like the Luminance component of CIE Lab normalized to 0.0-1.0 range. /pippin _______________________________________________ gimp-developer-list mailing list List address: gimp-developer-list@xxxxxxxxx List membership: https://mail.gnome.org/mailman/listinfo/gimp-developer-list List archives: https://mail.gnome.org/archives/gimp-developer-list
