yahvuu wrote:
> Chris Mohler schrieb:
>> I can express any CMYK color in RGB - but not the other way around.
> now i'm confused :)
> Is CMYK->RGB->CMYK roundtrip safe?

It depends on the gamuts of the respective colorspaces.
These are all device dependent colorspaces, so their
gamuts depend on the device in question. A gamut
can be described by a 3 Dimensional volume, and in
general two gamuts will have some region in common,
a region unique to one gamut, and
a different region unique to the other gamut.
This is often the case with RGB and CMYK
spaces (ie. sRGB and a typical offset press).

Whether CMYK->RGB->CMYK is roundtrip safe depends
on whether the RGB space fully encompasses the CMYK space,
or (if it does not), if the gamut mapping is being
reversed through the transformations.
Some people deliberately use a very large RGB gamut working
space to avoid clipping CMYK colors.

Note that by definition you loose the black inking information
though such a conversion, as well as a degree of fidelity.

A traditional graphic arts workflow often looks
something like:

   Capture in RGB

   Edit/adjust in RGB and/or Lab

   Convert/Separate to CMYK

   Adjust in CMYK

   Layout/Compose/Add non-image elements in CMYK.

   Convert to RGB for soft preview.

   Print the CMYK.

Although there are other more complicated ones,
including late binding (separating for the particular
output device after layout/composition).

Graeme Gill.

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