[borkin]

Dobur variant za "vruzvane" na dva CMYK profila c pomoshta na open source programa - www.argyllcms.com
Edna ot mnogoto opcii e da convertira korektno ot CMYK kum CMYK (vizh po dolu zashto - vupros i otgovor ot ECI Mailing List.)

N.B. Goliama chast ot help:a e online. Raboti v comanden red.

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From: Marttila Jouni
Hello List

Does anyone know a good source of information on Device Link Profiles. I
have made some tests with Device Link profiles made with PrintOpen but
PrintOpen documentation is quite "short" about the subject. Also it seems
that different programs offer different options. E.g. PM5 seem to offer
option that keeps also CMY "pure" when PrintOpen seem to keep only K "pure".

Any comments on the use and creation of Device Link Profiles is greatly
appreciated

Jouni Marttila
M-real

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From: Olaf Druemmer
Hi Jouni,

I believe the basic principle is relatively simple:

for any color appearance (let's assume it is e.g. expressed in Lab
values) there is more than one CMYK value combination for a given
printing condition that matches it (as closely as possible).

So going from Lab to CMYK a choice has to be made which CMYK combination
to use. The policies for such choices are expressed in the settings for
a profile making program (like PrintOpen or ProfileMaker), and this is
the setup for making regular separation profiles.

Now, if you already have CMYK for a given printing condition and need
CMYK values for some other printing condition, you could go through two
profiles - source CMYK profile and destination CMYK profile. Going from
source through PCS (profile connection space) to destination you'll get
new CMYK values. The way the new CMYK values are chose fully depends on
the separation settings in the destination profile, but it does not
depend at all on how the original CMYK values had been chosen (the
destination profile doesn't 'know' anything about the profile that had
been used to create the CMYK values in the source).

A device link profile incorporates a relationship between source CMYK
values and destination CMYK values in such a way that it 'knows'
something about the source CMYK values and _can_ maintain some
characteristics of them (e.g. a 0/0/0/100 black would remain more or
less a 0/0/0/100 black in the destination) while fine tuning others.
While doing so it nevertheless tries to maintain colorimetric accuracy
(which is possible as there is more than one CMYK value combination for
any given color appearance).

There is a number of 'fine tuning strategies', like maintain black
separation, maintain pure colors (where one of the four CMYK colorants
is used with a certain percentage whereas the other colorants are zero),
reduce ink coverage etc. It is impossible to achieve all possible 'fine
tuning goals' at the same time (as no degrees of freedom would be left).

Each of the tools that makes device link profiles has several options to
achieve certain 'fine tuning goals'. Exactly how they manage to achieve
them most probably is the secret of the maker of that tool. There is at
least one open source tool though (check out <www.argyllcms.com/>) which
may help you in getting hold of some of the internals of such a tool.

Olaf Druemmer
_________________
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