[argyllcms] Re: xicclu -g predictability issue

  • From: Elena [service address] <1007140@xxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 30 Jan 2011 20:03:02 +0100

Hello Gerhard

Just a quick answer for now. I have to reflect on your points some more. Also 
please
note that there're currently too many details of argyll I still miss.
One was for example the option -kl of xicclu which I never noticed.
Another is the difference between Locus and Value in argyll jargon, I maybe
stupid but I didn't understand it yet.

> While the "kz" locus is indeed smooth,

It is in fact. Softproofs from -kz profiles show quite no artifacts and are
very smooth. I however just discovered another gap of mine, till now I
misunderstood that -kz actually generated NO K at all. The big difference
from separation in greys (as shown by xicclu -g) and separation in color areas
once more misled me (and once more I kindly ask for the xicclu -p option or
call it how you prefer). But now I finally see the analogy with the Black
Width option of Profile Maker. Here Black is always wide. Being no such option
here (not that I want it, of course) I can well expect to see no K generated
in the greys but very much in the colors instead.

> the "kx" locus is discontinuous
> at two points. So any other black locus derived from the "kx" locus is
> supposed to be discontinuous too. But I'm curious where this "jump" is
> coming from. Is this just the result of inverting an almost flat, but
> still noisy/wavy region of the A2B table [i.e. a region which would be
> monotonically increasing or decreasing, if there weren't some ripples
> which break the monotonicity]?

I was always suspecting that.
It's one of the main reasons why in the beginning I was so concerned of starting
from a "proper" target - and of noise, averaging etc. I never believed that any
printer (unless deliberately driven in a discontinue way) can actually have a
potential gamut shape too discontinue and/or with holes or ripples or "islands".
Never believed!
My strong suspect is that argyll fails not just because it has no checks against
discontinuities, but mostly because the .ti3 is noisy, and/or not precise or
dense enough in some dark areas.
I still bet that supplying many additional CMYK patches in those troublesome 
areas
may result in serious improvements. Ok, but how to detect them ? It's not so
simple, expecially when it has to be done by hand...

/&

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