Re: [Groff] CMYK <-> RGB

[Werner LEMBERG]

> ... converting from CMY to RGB is straightforward.
> 
>     R   1   C
>     G = 1 - M
>     B   1   Y
> 
> Turning CMY into CMYK is similarly simple.
> 
>     K = min(C, M, Y)
>     C = C - K
>     M = M - K
>     Y = Y - K

This would imply for CMYK -> RGB the simple relationship:

  r = 1 - c - k
  g = 1 - m - k
  b = 1 - y - k

But the other formula gives

  r = (1 - k) * (1 - c) = 1 - c - k + ck
  g = (1 - k) * (1 - m) = 1 - m - k + mk
  b = (1 - k) * (1 - y) = 1 - y - k + yk

Apparently there is something which I don't understand...

Sorry for those basic questions.


    Werner