Re: [ECI-EN] Device Link Profiles

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 -- Olaf Druemmer | Managing Director callas software gmbh | Schoenhauser Allee 6/7 | Berlin | Germany Tel +49.30.44 39 03 10 | Fax +49.30.4 41 64 02 o.druemmer(a)callassoftware.com | www.callassoftware.com -- Simply good colors with pdfColorConvert plug-in for Acrobat - http://www.callassoftware.com/en/new_pdfcolorconvert.php Jouni.Marttila(a)m-real.com wrote Wed, 8 Feb 2006 09:35:10 +0200