[NTG-context] Issues with RGB to CMYK conversion with color profiles (was: Colormanagement)

Jan U. Hasecke juh+ntg-context at mailbox.org
Wed Nov 14 11:41:30 CET 2018


I forgot the archive. :-(

Am 14.11.18 um 11:39 schrieb Jan U. Hasecke:
> 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.
> 
> 
> There are several files in the archive:
> 
> The differences in the files are the color definition and the color
> profile used.
> 
> - rgb-xxx.tex – colors are defined with RGB values only.
> 
> - rgb-cmyk-xxx.tex – colors are defined with RGB and CMYK values.
> 
>   The cmyk colors are derived from the rgb values using gimp and the
>   color profiles sRGB/ISOCoated
> 
> - cmyk-xxx.tex – colors are defined with CMYK values only.
> 
> The xxx stand for two color profiles: iso-coated and swop.
> 
> What I see is this:
> 
> Colors in pdfs are the same no matter what color profile I choose.
> 
> With rgb values and rgb/cmyk values I get the same colors in pdf (the
> wrong ones).
> 
> With cmyk values only I get other colors in pdf. Next week my friend
> will test if these are the right ones.
> 
> I have many questions:
> 
> 1. Is colormanagement working in ConTeXt at all?
> 2. Is my code correct?
> 3. Why do pdfs with different color profiles show the same colors?
> 4. Why does ConTeXt not take the cmyk colors from \definecolor when
> there are rgb values as well?
> 5. Where can I define a coresponding rgb profile? In Scribus you have to
> define two profiles (eg. sRGB and ISOCoated) to make colormanagement work.
> 
> TIA
> juh
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