Dear Jan-Peter, You are 100% richtig: linearisation is paramount in printer profiling. > If a output-device behaves not linear, the number of patches for > profiling has to grow. Agree, but up to a point. Not so much because of more samples will not result in more exhaustive characterization but, read below. > In the case of inkjet printers, the linearity depends very much on the > limit for every CMYK-channel. True. > For every combination og paper an Ink, there is a point were more Ink > results not to more saturated color, but to huge shift in the Hue. True again. > The normal way to detect this, is to print steps from 0 to 100% of every > pure color, measure it and plot the results in an a-b diagram in the > Lab-colorspace. The point, were the hue began significantly to change, > is the point to set the inklimit for every channel. Yes, that is the correct analysis. And, as you point out, this presupposes having complete control of *all* channels. > After setting this limit, a 1-D LUT for every channel should calculated > which results to equal steps of the pure colors and a good > CMY-greybalance. Aha! I agree with the first part of your sentence but I cannot confirm the second part. Why? Linearizing each channels to perfection, however you want to do it, does not, in my experience results in CMY-graübalance. Ist das deine experienz? > For doing this step, softwares are using differnt > models. Das ist der "secret sauce". I wish I could compute this myself :( > Some are based on density, and some are based an Lab-values... Right. > In the last step, it is necessary to detect the max. inklimit / TAC > (Total amounf of color) for a given combination of paper and Ink. This > is mainly done by a visual inspection of a testchart where big patches > with different TAC an fine details are printed. If the fine details are > detroyed be "bleeding" og the big patches with a given TAC, this is > point to set the max. Inklimit. Good description again. > After this three steps, the testchart for profiling is printed. > In most cases a Testchart with e.g. 1485 patches like the ECI2002 gives > good results. Yes and no. I have an Epson 4000 here I'm profiling through PrintOpen v5, ProfileMakerPro v5.0.3, Monaco Profiler v4.7.2 and Fuji ColourKit v4.2 and it's never perfect. I always have to perform profile editing to get a good match. Why? I don't know. But there is something non-linear somewhere in the way these UC inks are mixing that defeats the profiler prediction. The following point is *very* well taken: > One last point to Epson Ultrachrome-printers: > For this printers, it is very hard to get a visual nice greybalance. How widespread is this view, Jan-Peter? No one on the ColorSync List ever admitted to this in public. I guess it depends on a lot of factors. Not so much the fact that the ink behavior is heavily metameric but the fact that, I suppose, a lot of people don't really notice it or complain about it. > I´m > getting significant better results by using a strong GCR starting at 0, > so that neutral tones are mainly rendered with black and light black. Well, this is what I've been lately experimenting with. Traditionnally, on all the inkjet printer I ever profile, I always used UCR. But I found it constrained me too much when editing the profile. So I started to use GCR. I can't say, however, that I find the graü balance better? > Such black generation can only be used, if the printer has additional > grey ink, Epson 4000 have Black and Light Black. > otherwise the strong black produces a "peppering" in > skin-tones (big black dots...) Yes, like Epson 3000. > greetings from europe > :-) Jan-peter Greetings from Kanada! Mfg, Roger Breton | Laval, Canada | graxx@xxxxxxxxxxxx http://pages.infinit.net/graxx