Yes, I think color conversions are that complex.
RGB was designed for monitors allowing a broad range of additive colors in the
form of light (i.e. lit pixels).
CMYK was designed for subtractive printing to paper offering a restricted range
of those colors; many of the RGB colors being "out of gamut" for CMYK, meaning
there is no formula to convert them.
Nobody serious is printing high-quality hardcopy using R, G, and B inks. And
I'm not sure why one would want to use CMYK to print to the screen.
Craig
> From: david.da...@non.schneider-electric.com
> To: framers@lists.frameusers.com
> Date: Wed, 22 Oct 2014 03:34:52 -0500
> Subject: RE: CMYK vs RGB RE: PDF query
>
> Are colour conversions really that "complex"?
> They're just converting colour coordinates in one colour-space to those in
> another, using some straightforward formulae that are hidden under the hood.
> (The choice of formula, and what to do if a colour is 'out of gamut', depends
> on the 'rendering intent', of which we usually have a choice of four).
> The conversions will give 'round-tripping' errors if they're out of gamut.
> This is why better Adobe software (Illustrator, Photoshop, InDesign) maps RGB
> and CMYK via a device-independent ("LaB") representation, rather than
> straight from one to the other.
> The problem with FrameMaker is that the conversion algorithms it uses are
> crude rubbish. This is why they frequently give such awful results, not
> because it's "complex".
>
> From previous threads on the Adobe Forums, it seems that the conversion
> formula Frame uses is:
>
> RGB to CMYK:
> C = max(R, G, B) - R
> M = max(R, G, B) - G
> Y = max(R, G, B) - B
> K = 100 - max(R, G, B)
>
> CMYK to RGB:
> R = min(100 - K - C, 0)
> G = min(100 - K - M, 0)
> B = min(100 - K - Y, 0)
>
> ...which gives rubbish results.
>
> David
>
> ____
>
> From: Jacob Sch?ffer (Grafikhuset) <j...@grafikhuset.dk>
> To: <i...@heiko-haida.de>, "'Craig Ede'" <craig...@hotmail.com>
> Cc: 'framers' <framers@lists.frameusers.com>
> Subject: RE: CMYK vs RGB RE: PDF query
> Message-ID: <00a601cfec93$39b38e10$ad1aaa30$@grafikhuset.dk>
> Content-Type: text/plain; charset="utf-8"
>
> It?s definitely NOT easy to explain this. Color conversions are COMPLEX.
> Anyway, RGB -> CMYK conversion is lossy, and CMYK -> RGB is also lossy.
>
>
>
> What is the point of the RGB switch afterall? Why not just pass through
> what?s input and remove this switch?
>
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