Am 2018-11-18 um 19:26 schrieb Hans Hagen
On 11/14/2018 4:51 PM, Wolfgang Schuster wrote:
Jan U. Hasecke schrieb am 14.11.18 um 11:39:
Hi all,
attached you find my colormanagement tests and I need your help to understand and debug the situation.
I am testing together with a friend of mine, a professional colormanager, who does not know ConTeXt. Even without a color profile the results from the normal conversion of colors from cmyk to rgb can result in differences between ConTeXt and Gimp because both use different formulas. This is the formula from ConTeXt (attr-col.lua) r = 1.0 - math.min(1.0,c+k) g = 1.0 - math.min(1.0,m+k) b = 1.0 - math.min(1.0,y+k) and this is the one from Gimp (https://gitlab.gnome.org/GNOME/gimp/blob/master/libgimpcolor/gimpcolorspace....) r = 1.0 - math.min(1.0,c*(1.0-k)+k) g = 1.0 - math.min(1.0,m*(1.0-k)+k) b = 1.0 - math.min(1.0,y*(1.0-k)+k) Are there more variants? Do we need to support variants?
Oh my, color separation is a science of its own, but not an exact science... Any really usable color conversion algorithm uses color profiles. It would make sense to outsource color calculations to a color management library like LittleCMS. Greetlings, Hraban --- https://www.fiee.net http://wiki.contextgarden.net https://www.dreiviertelhaus.de GPG Key ID 1C9B22FD