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

  • From: Alberto Ferrante <alberto.ferrante@xxxxxxxxxx>
  • To: "argyllcms@xxxxxxxxxxxxx" <argyllcms@xxxxxxxxxxxxx>
  • Date: Fri, 06 Sep 2013 12:14:52 +0200

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 1.6).

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

warm-up of the colorimeter:
targen -v -d3 -G -q -f5000 eizoCX240-riscalda
dispread -v -yb eizoCX240-riscalda

dispcal -t6500 -gs -b100 -qh -Yp -v -e1 -yb eizoCX240

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 profile)

B.t.w., thanks a lot for introducing the -Yp option!!

Best regards,

>> 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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