[NTG-context] definition and separation of colors

2010-11-16 Thread Henning Hraban Ramm
I stumpled upon a ambiguous color definition in my automatically  
generated documents:


\definecolor[Custom][c=0,m=1,y=0,k=0,r=0,g=0,b=0,]

I.e. the color is defined in CMYK mode as 100% magenta and in RGB as  
0/0/0 black.
In the PDF the color is shown as black, according to Acrobat's  
preflight defined as RGB 0/0/0; CMYK separation depends on the  
profile, e.g.:

Generic CMYK:76/71/65/81
ISO Coated FOGRA27:  86/85/79/100
Euroscale Coated:95/83/82/90
(I didn't expect the Euroscale Coated profiles to differ that much!)

If I say \setupcolors[rgb=no], I get CMYK 100/100/100/0.
This is not a good separation algorithm - GCR or UCR would be nice,  
but at least RGB 0/0/0 should render as CMYK 0/0/0/100.
(Perhaps you could include something like littleCMS in LuaTeX and even  
deal with images?)


It doesn't change if I define in different order, like  
\definecolor[Custom][r=0,g=0,b=0,c=0,m=1,y=0,k=0,]

I get magenta only if I leave out the RGB values.

It seems that in ConTeXt the RGB definition always takes precedence?  
Is this intended?



Greetlings from Lake Constance!
Hraban
---
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http://wiki.contextgarden.net
https://www.cacert.org (I'm an assurer)

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Re: [NTG-context] definition and separation of colors

2010-11-16 Thread Hans Hagen

On 16-11-2010 9:37, Henning Hraban Ramm wrote:

I stumpled upon a ambiguous color definition in my automatically
generated documents:

\definecolor[Custom][c=0,m=1,y=0,k=0,r=0,g=0,b=0,]


you should not mix definitions (so, either cmyk or rgb or g of h of hsv 
keys)



It seems that in ConTeXt the RGB definition always takes precedence? Is
this intended?


just a side effect of definitions

when a rgb color is defined, internally conversions to cmyk and gray 
take place and depending on the color space one of them is used


when an cmyk color is defined, 

Hans


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