[argyllcms] Re: Argyll 1.5.1: artifacts in dark shadows - It got worse in 1.6!

  • From: alberto.ferrante@xxxxxxxxxx
  • To: <argyllcms@xxxxxxxxxxxxx>
  • Date: Thu, 10 Oct 2013 15:50:40 +0200


Dear Graeme and all, 

yesterday I was able to do some further
experiments and I have discovered that by using the -q u option in
colprof almost all artifacts disappear. I just have some strange line on
a very dark background, but it is much better than with -q h (-q m and
-q l give reddish artifacts in the dark gray shadows). I tried to use -q
u in colprof 1.4 and I got no artifacts and, in fact, the profile looks
better than the one obtained by using -q h (I haven't had time to do any
measurement though). 



Alberto Ferrante wrote: 

Dear Graeme,
> you are right: it was some months ago and I should have
summarized the
> history of this problem in my previous message, sorry!
Let me do it now.
> I will start by replying to your question: Since
Argyll 1.5 I started
> experiencing the problem of artifacts in the
shadow areas. After some
> tests we discovered that the problem was in
the modifications to the
> algorithm used to compute curves in the area
near black that have been
> introduced in colprof 1.5. Since we could
not solve the problem (though,
> the profile generated by using the
"test" version of colprof 1.5.2, if I
> remember well, was a bit better
then the one generated by using 1.5.1),
> I kept using all the
up-to-date tools of Argyll except colprof. I was
> successfully using
colprof 1.4.x to generate my profile. I now see,
> that, by mistake, I
updated Argyll from the Fedora repository:
> therefore, I wasn't using
colprof 1.4 anymore, but 1.5.1: sorry, my
> mistake! It may well be that
by using colprof 1.4 I can still generate
> good profiles even with the
other tools from argyll 1.6, I will test
> that! It remains the fact
that the problem seems to be worse in 1.6
> (i.e., when using colprof
> About the whole story: I sent to you test images, the
profile, and the
> data used to generate this profile. You could
reproduce the problem,
> but, unfortunately, you could not find a
solution to it. Actually, I
> have to say that I had similar problems
(but not with shadows, with
> bright red) on another monitor (the one of
my laptop). My impression is
> that (but I might be completely wrong!)
sometimes targen generates
> patches that are outside the gamut of the
monitor (or, maybe, too close
> to the limits), even though a reference
profile is provided by using -c.
> This causes the final profile to try
exceeding the monitor capabilities
> (and this, of course, also depends
on colprof). Most of the times,
> changing the algorithm for generating
the patches improves things (on
> the laptop I am now successfully using
-r). Yesterday night I applied
> the same strategy on my main monitor
and, by using -q in targen, I
> almost completely solved the problem. My
current calibration flow is as
> follows:
> warm-up of the
> targen -v -d3 -G -q -f5000 eizoCX240-riscalda
> dispread
-v -yb eizoCX240-riscalda
> calibration:
> dispcal -t6500 -gs -b100
-qh -Yp -v -e1 -yb eizoCX240
> profiling:
> targen -v -d3 -G -e8
-g32 -q -c eizoCX240.icc -f4096 eizoCX240
> dispread -v -yb -Yp -k
eizoCX240.cal eizoCX240
> colprof -A "Eizo" -M "CX240" -D "$d - $s" -v
-q h -d mt -aX eizoCX240
> (eizoCX240.icc is the previous month
> B.t.w., thanks a lot for introducing the -Yp option!!
Best regards,
> Alberto
>>> Hi all,
>>> sorry to bring this old topic
up again, but I was doing the
>>> monthly re-calibration of my monitor
and I noticed that, by using
>>> Argyll 1.6, the problem with dark
shadows got worse. I now obtain
>>> artifacts even by using colprof from
Argyll 1.4 (which was not the case
>>> before) and the artifacts are
much more evident. Artifacts now seem to
>>> disappear (I have to check
again more carefully when I get home
>>> tonight, though) by using -al
instead of -aX.
>>> Is there anything I can
>>> do to help solving this
problem? Last time we could not find a solution
>>> to it.
>> Hi,
I'm not really following you. How can Argyll V1.4 be affected
>> by
changes in Argyll V1.6 ???
>> I don't really recall where we got to
last time, whether the problem
>> was resolved, or whether I was unable
to reproduce it.

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