Re: Metapost and CMYK

[Hans Hagen <pragma@wxs.nl>]

Peter Rolf wrote:
> luigi scarso wrote:
>   
>> On 2/2/07, Peter Rolf <indiego@gmx.net> wrote:
>>     
>>> Hi all,
>>>
>>> I have some questions about cmyk in combination with Metapost. Just by using
>>>
>>> \setupcolors[state=start,
>>>   cmyk=yes,
>>>   mpcmyk=yes,
>>>   rgb=no,
>>> ]
>>>
>>> I get cmy(k=0) graphics, although all used colors are still defined in
>>> the rgb color space.
>>> This is really a nice feature and the automatic color conversion works
>>> relative good. Only (so far I have seen) gray tones have a noticeable
>>> tendency to brown (Acroreader 7.09). I have tested one of those gray
>>>       
beware, without black component, on paper one indeed get brownish 
colors. acrobat reader tries to mimick paper (can be configured) so this 
is why you don't get gray on screen

when converting colors to gray context does weighted conversion (as with 
b/w televisions) so 1,0,0 and 0,1,0 give different grays

>>> tones by defining it as cmyk and the result looks ok.
>>>
>>> RGB(223,223,227)
>>> CMY(0.12548, 0.12547, 0.10980)
>>> CMYK(0.01762, 0.01760, 0, 0.10980)
>>>
>>> So is there a way to get cymk instead of cmy?
>>>
>>>       
>> hmm,
>> can you post an example ?
>>
>>     
> Mojca has pointed me to the definition of
>
> \convertRGBtoCMYK (colo-ini.tex)
>
> and (if I understand it right) this is only a
> RGB->CMY conversion.
>
> The algorithm for the missing CMY->CMYK conversion is simple (see
> http://www.easyrgb.com/math.php?MATH=M13#text13 ),
> but "exact" calculation in TeX is no fun at all (at least not for me).
> I have tried to implement it, but yet without success. In the worst case
> I have to wait for luatex, which will solve all calculation problems.
> So think twice, before you waste your time... ;)
>
> Maybe I should add this color conversion to the feature request list, so
> that it will not be forgotten?
>
> Peter
>
>   
>> luigi
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>>     
>
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