[argyllcms] Re: Black turning down problem - help!
- From: Elena [service address] <1007140@xxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 07 Jan 2011 13:54:37 +0100
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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