Thomas, Neil and list - on the deep and confusing topic of Photoshop Duotone mode...(where do I begin <g>?). I do not have a direct answer - but perhaps my ramble will make a 'light bulb' pop on over someone's head. <g>
Here is a quote from Thomas Knoll when I quizzed him on some very tough questions on the why and how of Duotone mode last year: "The preview simulation of duotone files is only approximate at best. Duotone mode were never intended to act as an editing mode for files that will primary be output to a CMYK or RGB printer. Expecting accurate proofs of duotone mode documents on CMYK or RGB devices is expecting far too much from Photoshop's duotone mode, given the very limited amount of information it has about ink interactions." D/tone mode predates ICC CM and is not a work space, but a device space with no real support for accurate conversion to other spaces. Current ICC profiles do not support duotone mode (and Duo does not support ICC) and Thomas Knoll said it may take up to four profiles to accurately describe a duotone mode file with a clunky four profile mismatch dialog box, depending on how users choose their ink builds. <g> Duotone mode is a simple concept when used as originally intended - all you do is output separations and you get the correct results. That you can also have a colour composite preview/print is nice, but not the intended goal of the process and this is not really set-up as we would expect (we are in device space). One should give forethought and care to how one defines the ink colour build in Photoshop for the Duotone colour in question, although Adobe do not spell this out and even with over ten years use I did not fully understand all the issues until Thomas Knoll pointed them out. Entering LAB values for the colour in question seems the safest approach (if you choose a custom PMS colour then go into the picker and hit the LAB button and retype the LAB values over themself ). With this approach, in v5.x the LAB gamma display/conversion values are tied to the dot gain of the current CMYK work space K channel but the colour is device independent based on the LAB build. In v6 it is the new Spot dot gain WS that is used for display of tone but not colour, which is LAB. If you choose a built in custom colour library (v6 or earlier) or an installed colour book (v7) then the colour description of that ink may be a LAB, CMYK or LAB/CMYK hybrid description. If you use the colour picker to enter RGB values, then the colour is tied to the current RGB work space (same for CMYK mode). What this means is that if you change RGB or CMYK descriptions then the assumed colour of the Duotone build will change, as well as it's luminance. If you build a two ink file with one ink with RGB picker values, and the other with CMYK picker values - then both RGB and CMYK WS settings affect the Duotone mode display and conversion in Photoshop...or perhaps any other possible combination of builds... Even with all this confusion - the actual separation values which are a combo of the original greyscale files tones and the Duotone mode transfer curves are not affected. Adobe never intended this mode for composite work. This is only the Photoshop side of things, as when converting from Duotone mode to a regular composite mode. Then one must consider how the colour contained in the Duotone EPS file is used in other software. This can add more confusion... When you select a custom colour such as Pantone Coated in the Duotone ink selector, it will list a default build - either in LAB or CMYK values depending on the library. Commonly most Pantone are LAB/CMYK hybrid and imported images assume CMYK numbers as the description to fit the standard non ICC colour managed prepress workflow. When it comes to ICC colour managed digi proofing a true wider gamut representation of the colour in question, the mystery meat CMYK will probably not do it and you would need a Pantone source CMYK profile or something which I know nothing about <g>. In my limited experience some RIP's can see the named colour in the PostScript print data and call upon a library to supply a wide gamut LAB colour as the source for the spot ink and not use the CMYK description of the numbers in the file. Perhaps some software can read LAB values in the EPS file and not assume them as CMYK builds for the inkset, I don't know. But this does not mean that an accurate simulation of a press or proofing condition which has it's own characteristics when these two or more inks are mixed with a certain stock etc. Close to accurate solids spot colour is one thing, Duotone mode is another game. That's enough for now - each time I post on this topic I can answer better than before, but I always find myself asking new questions and having more doubts than a firm grip on what is taking place. <g> Stephen Marsh. =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
