Glen Berry wrote:
> 
> Aren't CMYK>RGB and RGB>CMYK difficult conversions? 

No, basically this are as easy as that (RGB->CMY):
C = 1 - R
M = 1 - G
Y = 1 - B
In case of CMYK K is computed as minimum from C,M,Y and each component
(CMY) is reduced by this value.
This "easy" conversion works in theory, in practice it's much more
complicated (see below).
> If I understand it
> correctly, there are skilled photographers who own Photoshop and still
> send files to professional service bureaus for such conversions, in
> preparation for high-quality printing. I think that these bureaus
> often have to make manual corrections, to optimize the conversion. I
> think it has to do with the idiosyncracies of printing inks and
> printing technology.
> 
You are correct. colorspace FAQ has more detailed explanation for it,
basically it comes down to the fact, that ink spectral absorption curves
overlap and thus this easy CMY = 1-RGB doesn't hold. Other problem is
non-linearity by dot gain, causing similar problems as gamma in case of
monitors.

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