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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In article <3911596B.FB7BB83F@aetec.ee>, Vahur Krouverk 
<vah### [at] aetecee> wrote:

> > Is this colorspace FAQ available online?
> > 
> Yes, there->
> http://www.faqs.org/faqs/graphics/colorspace-faq/

Thanks!

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/

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In article <39115C75.19BC1A37@aetec.ee>, Vahur Krouverk 
<vah### [at] aetecee> wrote:

> 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.

Ok, then there already exists a filter which can do most of the 
conversion: invert. You could then get K using the "min" filter.(which I 
haven't written yet)

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/

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[Vahur Krouverk <vah### [at] aetecee>]
| No, I'm not going to support CMYK. There is number of reasons:
| Firstly, because RM SL does not support it (it supports 6 above
| mentioned color spaces, AFAIK) and I want to make this patch as
| compatible with RM as it would be possible.
| Secondly, I don't think, that CMYK is needed for POV-Ray. If someone

Too bad POV-Ray doesn't support colors outside of the RGB-cube, like
the LAB-format, which contains all colors visible to the human eye,
like blacklight and other neat colors your monitor can't display.
Of course, since no commercially available display exists to show the
darn image, and certainly no printer that can print it, it's rather moot.

-- 
A penny for your thoughts.
Mine are more expensive.

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