Re: Issues with RGB to CMYK conversion with color profiles

[Hans Hagen <j.hagen@xs4all.nl>]

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


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