[argyllcms] Re: Purplish blues with Perceptual in Argyll 1.1.0_RC1

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 28 Nov 2009 10:03:52 +1100

Elena [service address] wrote:
1) With Perceptual, the RGB pure Blue comes out really purplish rather than
   blue, a very annoying thing. With RelCol, it comes out plain blue, i.e
   what it should be (sorry if I can't attach a scan, my scanner should
   be profiled better still, currently it isn't able to show very much
   this purple cast in blues).

I think that V1.1.0 RC1 does have this tendency more than 1.0.4, but
it depends a lot on the shapes of the two gamuts involved. I'm working
on RC2 in light of various feedback, and intend to increase the hue
error weight, so that the RC2 result in this respect should be much
closer to 1.0.4.

3) A pity, Argyll profile still has "bumps",or "waves", expecially noticeable 
   printing out fully saturated RGB test fades, HUE circles and such things. If 
   don't understand what I'm meaning, it's the same problem discussed in
   a past topic

My experience with this is that it's a combination of both the profile
itself (per channel curve shapes, clut grid resolution) and the black
generation parameters being used. Changing the black generation
curve shape can have a big influence on the bumps, so it's worth
exploring the settings using xicclu -g, and then re-creating
the profile. Basically the current algorithm doesn't make
any attempt at guaranteeing black smoothness (or putting it
another way, minimizing dramatic changes in the ink
combinations), so choosing a black curve that is sympathetic
to the values at the gamut edges helps minimize the "bumps".
Increasing table resolution helps too, but at the cost of
processing time.

   Oh, also I actually was unable to go beyond -qm because with -qh my PC is
   still calculating the profile after several hours (don't know if that's
   the expected behaviour... it's a Win XPPro machine with P4 dual core 3Ghz, 
   really crap...)

It can be slow, depending on the nature of the device and the size of the
profile. One thing to check is whether your machine is running out
of memory and swapping to disk. This makes things very, very slow.
Basically Argyll assumes that most of the memory is available to it,
and attempts to use as much as possible to speed things up.
If there are other applications present that are also using
noticeable chunks of memory (ie. Firefox etc. is pretty bad),
then Argyll will start to swap. Looking at the performance
monitor will give you a hint - if one CPU is not at 100%,
then it's swapping. In this case you either need to
shut down other applications, and/or reduce the amount
of memory Argyll is attempting to use by setting the
ARGYLL_REV_CACHE_MULT environment variable to a value
less than 1.0 (See <http://www.argyllcms.com/doc/Performance.html>).

        Graeme Gill.

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