On 03/22/2011 01:37 AM, Jacek Poplawski wrote:
> On Mon, Mar 21, 2011 at 11:30 PM, gespert...@gmail.com
> <gespert...@gmail.com>  wrote:
>> Most of the people ask for CMYK because:
> I need CMYK support for photo retouch, to create better colors.
> CMYK is no different than LAB, HSV or RGB. It is colorspace like
> others, but uses 4 channels instead 3.

CMYK is fundamentally different than LAB, HSV and RGB.

In order for RGB values to make colorimetric sense, meaning that the 
CIEXYZ tristimulus values are known, all you need to know are the 
primaries and the white point used.

The tristimulus values for a set of CMYK values depends on the 
characteristics of the pigmets, the pattern in which the colorants are 
arranged on paper, the order in which they are applied, the illuminant 
used, the characteristics of the paper they are applied on, and even the 
age of the print.

Another difference of the CMYK color space compared to e.g. RGB is of 
course it's subtractive nature, meaning that as you increase CMYK 
values, the resulting color will be darker, whereas with RGB, larger 
values means a brighter color.

HSV is just a different representation of RGB values, and LAB values 
makes colorimetric sense by themselves, without any additional information.

That CMYK is fundamentally different than light based additive color 
spaces is the reason why GIMP developers considers CMYK somewhat of a 
special case we can take care of later, we first need to make a program 
that is powerful in the additive color space world.

  / Martin


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