Hello! I've often struck with similar problems while CMYK profiling. There is one way with Argyll - to play with ink limits and -Kp or -kp parameters. I've played with Elena's ti3 data and have built rather smooth profile with heavy black generation. My command lines was: spec2cie -f -i D50_1.0.sp -o 1931_2 -n 2xOFPS.ti3 2xOFPScie.ti3 colprof -v -al -qh -Kp 1 0 1 0.6 0.55 -L90 -l285 -r 0.85 -s sRGB.icm -dpp 2xOFPScie See attached graphs, relative.png and perceptual.png. Fri, 07 Jan 2011 13:54:37 +0100 письмо от Elena [service address] <1007140@xxxxxxxx>: > Hello Graeme > > On 7-Jan-2011, Graeme Gill wrote: > > > Yes, this sort of thing does happen. The CMYK 4 dimensional hyper-cube gets > > folded into 3 dimensions. If the device is well behaved, the CMY+100%K cube > > completely contains the CMY cube. If it does not (and in your device at > least > > the CMY corner pokes through the CMY+100%K cube), then the topology > > is quite difficult, and Argyll's current code doesn't attempt to > > solve this problem automatically. > > And I wouldn't even be able to suggest you how to solve it. These things > shouldn't really happen. It would be interesting to know, however, how > other profilers work out this condition. As soon as I have additional time > I will try PM to see what comes out (I never made plain paper profiles with > PM). > > > Even with the best possible > > setting of the black curve, there will be problems where the sides of > > the CMY cube penetrate the CMY+100%K curve, and the maximal gamut > > surface suddenly changes K value. > > The matter, however, is that no artifact should be visible. I will try today > to see what happens with a profile made out of some 3000 patches and -qh > > > Given that you've discovered this, it might be best now to take > > Rogers advice and move on to better behaved media (assuming that > > the current paper is not your real aim). > > It's not my real aim, but I admit that I sometime missed a good plain paper > profile in my pocket, when you happen to need a quick print on plain paper > for some purpose. > Well, the most important thing however is having understood the problem. > Now it's to my science and creativity to see how to solve it, if necessary. > > A stronger black ink would surely improve things here in many cases. > After all, why they invented the CMYK system ? Mainly for text, because > often CMY alone can't offer a neutral and deep black (also for possible > smudging > or register problems). But when the used K is actually weaker than CMY, > one would have the temptation to simply drop it :-D > > > No, that's not how it works. -k sets a target K ink value. -K sets > > a value between the minimum and maximum possible K ink values (the "locus") > > at each and every point. That was my first approach, but in practice > > I found it was very difficult means of setting a usable black curve, > > hence it relegation to a test option. > > I noticed that -K sometimes offers smoother results, but it's not a rule > > bye > /&
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