I was curious as to why the Babl/Gegl/Gimp code uses the unadapted sRGB luminance values rather than the adapted values. Quoting Lindbloom (http://www.brucelindbloom.com/index.html?WorkingSpaceInfo.html): Since the ICC specification and Adobe Photoshop both use a reference white of D50, the working space primaries that are specified relative to some other reference white must first be adapted to D50 before they may be used in a D50 environment, or be meaningfully compared with one another. If I understand him correctly, Poynton (http://www.poynton.com/PDFs/ColorFAQ.pdf) was talking about the conversion appropriate for sending signals to a monitor with a D65 white point. Y709 = 0.2125 R + 0.7154 G + 0.0721B Lindbloom unadapted and adapted sRGB "Y" values: unadpapted sRGB R, G, B luminance (Y): 0.212656 0.715158 0.072186 adapted sRGB R, G, B luminance (Y): 0.222491 0.716888 0.060621 The sRGB profile created in gegl/operations/external/lcms-from-profile.c has values very close to the Lindbloom adapted values: 0.222488 0.716904 0.060608. All the code in Babl/Gegl/Gimp that I could locate uses values very close to the Lindbloom *un*adapted Y values: ./babl/babl/base/rgb-constants.h: #define RGB_LUMINANCE_RED (0.212671) ./babl/babl/base/rgb-constants.h: #define RGB_LUMINANCE_GREEN (0.715160) ./babl/babl/base/rgb-constants.h: #define RGB_LUMINANCE_BLUE (0.072169) ./gegl/operations/common/snn-mean.c:#define RGB_LUMINANCE_RED (0.212671) ./gegl/operations/common/snn-mean.c:#define RGB_LUMINANCE_GREEN (0.715160) ./gegl/operations/common/snn-mean.c:#define RGB_LUMINANCE_BLUE (0.072169) ./gegl/operations/workshop/snn-percentile.c:#define RGB_LUMINANCE_RED (0.212671) ./gegl/operations/workshop/snn-percentile.c:#define RGB_LUMINANCE_GREEN (0.715160) ./gegl/operations/workshop/snn-percentile.c:#define RGB_LUMINANCE_BLUE (0.072169) ./gegl/opencl/colors.cl.h:" #define RGB_LUMINANCE_RED (0.212671f) ./gegl/opencl/colors.cl.h:" #define RGB_LUMINANCE_GREEN (0.715160f) ./gegl/opencl/colors.cl.h:" #define RGB_LUMINANCE_BLUE (0.072169f) ./gimp/libgimpcolor/gimprgb.h:#define GIMP_RGB_LUMINANCE_RED (0.2126) ./gimp/libgimpcolor/gimprgb.h:#define GIMP_RGB_LUMINANCE_GREEN (0.7152) ./gimp/libgimpcolor/gimprgb.h:#define GIMP_RGB_LUMINANCE_BLUE (0.0722) ./babl/extensions/ycbcr.c: luminance = 0.2126 * red + 0.7152 * green + 0.0722 * blue; ./babl/extensions/ycbcr.c: luminance = 0.2126 * red + 0.7152 * green + 0.0722 * blue; ./gegl/operations/common/svg-saturate.c uses red:0.213 green:0.715 blue:0.072 Elle -- http://ninedegreesbelow.com Just because it's a standard, doesn't mean it's right. _______________________________________________ gimp-developer-list mailing list List address: gimp-developer-list@xxxxxxxxx List membership: https://mail.gnome.org/mailman/listinfo/gimp-developer-list
