<x-flowed>At 12:09 PM +0100 7/31/01, Rew, Alan wrote: > >Can one of our CM gurus please comment on this - if the light and dark inks >(e.g. the C and c inks on my 1200) can produce <different> hues on a paper, >doesn't this make profiling such a printer fundamentally difficult, or maybe >impossible sometimes? Difficult, yes. >This sounds like a theoretical nightmare, especially >as the relative proportions of the light & dark inks will vary depending on >the precise hue to be printed. It can be twisted and I mean that literally. In theory, the light c and m inks would be the same hue and when blended in the driver/RIP, would not enter into the CM equation. In reality the blending itself is rarely taken into consideration except in some RIPs where you can control how they blend. Ultimately it is important to remember that ICC profiling is based on the appearance of colors and how they relate to the RGB, CMYK, CcMmYK, CMYKOG or whatever ink combinations that may create them. If we built absolutely massive profiles where each color was sampled & stored along with the ink formulation that produced it then the number of channels controlling the printer would not be too much of an issue (although black generation is something that will always be nice to have control over). In reality we don't have that many values. Profiles are built from 200-1000 (typically) patches that are interpolated into 3-D tables (for output at least). Even a small table with 15 divisions per side has 15x15x15 (>3000) values in it. So the profiling software interpolates to create the table. Then we come along with a color that doesn't fall right on a grid line (with a printer gamut containing 500,000 to 1,500,000 possible Lab values it's not too hard) and the CMM is forced to interpolate again. Now, if you had a 6 channel printer, you would have more criss-crossing lines in the table to "guess" at the best ink combination for the color. If you only had 3 lines to choose from you could not possibly get as close. I described it a while back in relation to an octopus marionette. Ideally, you would want to have an 8 or 9 string control for that octopus but that could get unwieldy (not being as well endowed as our undersea friends in the arms department). You could control the marionette with three strings and probably make a pretty convincing octopus, but the more strings the better. Strange, late-night ramblings I know but I hope I shed a little light on it. Regards, Steve Upton +--------------------------------------------------+ Steve Upton upton@chromix.com CHROMiX / Profile Central www.chromix.com www.profilecentral.com p:206-985-6837 f:206.526.8278 9594 1st Ave NE #390 Seattle, WA 98115 Color Store...Remote Profiling...Media Management +--------------------------------------------------+ -- - Turn off HTML mail features. Keep quoted material short. Use accurate subject lines. http://www.leben.com/lists for list instructions. </x-flowed>