[NTG-context] Issues with RGB to CMYK conversion with color profiles

Hans Hagen j.hagen at xs4all.nl
Sun Nov 18 19:26:41 CET 2018


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.c) 
> 
> 
> 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?

Hans


-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------


More information about the ntg-context mailing list