what is algorithm of photoshop for converting rgb to cmyk as percentage? [duplicate]

Question

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CMYK to RGB formula of Photoshop (3 answers)

Closed 9 years ago.

what is algorithm of photoshop for converting rgb to cmyk as percentage ?

for example:

R   G   B      C    M    Y    K
0   0   0   => 75%  68%  67%  90%
3   0   0   => 100% 100% 100% 100%
149 91  56  => 32%  65%  84%  21% 
255 255 255 => 0%   0%   0%   0%

I'm using javascript

Answer 1

RGB is converted to CMYK and vice versa by profile through CIE-Lab values.

CIE-Lab is a kind of "universal" color space connected to what people see by eyes.

Color properties of R, G and B values are contained in concrete RGB profile, and CMYK properties are contained in concrete CMYK profile as well as method how situations when one color can be obtained by different CMYK combinations should be resolved.

Some profiles have formulas, some profiles have interpolation matrix obtained by calibration.