[argyllcms] Re: Argyll, ColorMunki & dual display

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 22 Sep 2010 10:44:08 +1000

Kai-Uwe Behrmann wrote:

The nvidia propriarity driver works perfectly with Compiz and thus with the CompIcc plugin[1]. A distribution like openSUSE allows to install all needed components per thierd party repositories. A LUT setup is not desireable with this setup. The ICC profile does the calibration and colour correction through GPU texture shaders in one step. The drawback is that all applications see currently only the desktop document colour space, which is sRGB. Applications have to be updated before they can use the native device gamut again.

Hello Kai-Uwe,
        while this setup will certainly allow color management
to be used and applied to all applications on the desktop, it
has several drawbacks:

1) The application has little flexibility as to how it handles the color.
   Either it's stuck with sRGB, or double color correction is applied.

2) The gamut is limited to sRGB (or some other chosen colorspace), rather
   than the full gamut of the monitor being available to the application.
   This can be significant in proofing situations, particularly if
   optimized proofing device links are being employed.

3) Profile based color management usually doesn't allow manipulating
   the white point and brightness level of the display, while calibration
   using per channel LUTs does. These aspects can be important in
   soft proofing situations.

4) Per channel calibration LUTs have far greater precision than profiles,
   and are therefore able to make fine corrections to the transfer curve,
   particularly near the black point and in setting the white point.
   This is primarily due to the number of measured patches involved in
   calibration vs. profiling, and the dimensionality of the spaces being
   explored. In addition, while a one step texture lookup will be good for
   applying 3 dimensional colorspace and gamut transformations, it
   won't have the same precision as a separately applied per channel
   curve lookup.

Note that if the per-channel hardware LUTs are not available for
particular cards, it's still perfectly possible to profile them, and 
can make use of those profiles. While this still has the same drawbacks of
not using calibration curves that the plugin mentioned above has, it
has the advantage of making the full gamut of the display available
to the application.

In case nouveau can be setup with Compiz, the compIcc colour server plugin should work with nouveau too.

Nouveau is certainly worth checking out to see if it solves this problem
while not introducing significant limitations for your typical uses.

Graeme Gill.

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