[argyllcms] Re: Calibration + profiling or Profiling only

  • From: Kai-Uwe Behrmann <ku.b@xxxxxx>
  • To: ArgyllCMS <argyllcms@xxxxxxxxxxxxx>
  • Date: Tue, 14 Sep 2010 07:49:26 +0200 (MEST)

Date: Mon, 13 Sep 2010 11:14:08 +0200
From: =?ISO-8859-1?Q?Florian_H=F6ch?= <lists+argyllcms@xxxxxxxxx>
Subject: [argyllcms] Re: Calibration + profiling or Profiling only

I haven't really looked into it in detail, so I can't really compare to
yCMS. Also keep in mind that depending of the type of ICC profile you
use (LUT or shaper/matrix), you tend to sacrifice smoothness over
accuracy (if using a LUT profile) or vice versa (if using a matrix one).
It all comes down to in which area you're most willing to compromise.

The following comment is not much related to video, as that is for home users often in the 8-bit per channel (bpc) domain.

On a 8bpc system the only way to pass data and its inherent precission to the monitor is the graphics cable. If the graphic card is set to handle calibration in the 8bit domain as with typical vcgt tags, the available tonal range is neccessarily shrinked to below 255 steps as tonal steps get lost during the 1D lookup.

Applications, which are able to do the colour correction directly from higher bit depth sources can provide smooth data, and I mean tonal saturated for the lower 8-bit domain, to the digital graphics cable connection. The 'vcgt' determines then the limit. Typical higher bit depth sources are OpenGL content, some painting applications and CameraRAW or medical imagery.

So I would suggest to skip the calibration in favour to not close the door for the capable applications if they are going to be used on a given system. With a desktop colour server like CompIcc the whole display is colour corrected. The video card gamma table is then obsolete anyway. (I wonder why on osX SL, which desktop has colour server capabilities, the monitor ICC profiles still have embedded 'vcgt' tags. A bug?)

kind regards
Kai-Uwe Behrmann
developing for colour management www.behrmann.name + www.oyranos.org

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