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

Hello Joune From my personal view, the combination of standardization and devicelink-technology is the best solution for: - Buidling colorservers for printdata which adresses reliable and fully automated colortransformations for both vector and images. - Using a standard colorspace like ISOcoated as master-colorspace, makes it possible to build preconfigured colorservers, which transforms ISOcoated CMYK-PDF/X to other ISO-standards. - The german company impressed www.impressed.de already offers precalculated devicelink-profiles for doing this, which can be used with PDF-colorservers in a Range from 300,- to 4000,- EUR (sorry, but there is NO english information on the website about it) Originator of the devicelink-profiles is http://www.colorlogic.de which has very little english informations about it yet. I myself did some consulting to colorlogic for settings and quality-control for producing this devicelink-profiles... Possible PDF-colorservers for devicelink-profiles are: Alwan ICCprofile Processor http://www.alwancolor.com Apago PDFenhancer http://www.apago.com Callas pdfColorConvert (AcrobatPlugIn) http://www.callas.de Callas pdfColorConvert (CLI-Version)http://www.callas.de Heidelberg Prinect ColorEditor http://www.heidelberg.com GMG Colorserver (ICC-DeviceLinks must be converted to internal GMG-format) http://www.gmgcolor.com CGS ORIS works / pressmatcher / PDF-Tuner ICC-DeviceLinks must be converted to internal ORIS-format)http://www.cgs.de GMB iQueue (only MacOS 9...) - In a printing house, devicelink-profiles are ideal, to convert/optimize delivered ISO CMYK-PDF/X-data to an internal printing standard. - Limiting the TAC without changing colorors beyond the maxTAC is easy with appropiate devicelink-profiles. This is e.g. the easiest way for a weboffsetprinter to limit ISOcoated-data to maxTAC of 320. - Changing the black generation for saving Ink is another solution, which often is used at weboffset-printers. A complete solution, which offers dynamic devicelink-creation for - colorconversion - TAClimiting - INksaving include preflight for TAC and a PDF-colorserver is Alwan CMYKoptimizer. http://www.alwancolor.com Another solution for static devicelink-creation, powerful editing-tools and a integrated PDF-colorserver is the gmgcolorserver I already mentioned. My personal preferred tools for creating static ICC devicelink-profiles for optimizing print-data are Alwan Linkprofiler: http://www.alwancolor.com colorlogic CoLiPri: http://www.colorlogic.de (actual very pure english documentation, but very powerful incl. finetuning devicelinks with photoshop) Even if i use GMB Profilemaker and Heidelberg PrintOpen regularly, I don´t recommend the their devicelink-options. Both solutions don´t provide all necessary options I need to do my jobs. e.G. - the Profilemaker-Module don´t delivers limiting of TAC, if preserve separations mode is active - Heidelberg PrintOpen has no possibility to preserve pure colors. One general open point in the whole ICC-Colormanagement is the question of the smoothness of a complete colortransformation from source to destination, which can be made with two ICC-profiles or one devicelink-profile. After free registering under http://www.devicelink-colormanagement.com (actually all stuff only in german...) You can download testimages to inspect the smoothness of CMYK 2 CMYK colortransformtions at http://www.devicelink-colormanagement.com/Testdateien :-) Jan-Peter Marttila Jouni wrote: -- -- homann colormanagement ------ fon/fax +49 30 611 075 18 Jan-Peter Homann ------------- mobile +49 171 54 70 358 Kastanienallee 71 ------- http://www.colormanagement.de 10435 Berlin --------- mailto:homann@colormanagement.de