[argyllcms] Re: Xorg video card lookup tables, tone response curves, etc

  • From: Gerhard Fuernkranz <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 14 Apr 2008 22:54:36 +0200

Samer Abdallah wrote:
> I think it would make much more sense to throw out the Gamma
> calibration model and bizarre nonlinear RGB spaces and calibrate to
> log-intensity instead,

IMO this is also a matter of the particular viewing conditions.

Under the assumption that the observer is constantly adapted to "display
white" I don't think that a log response makes too much sense,
particularly not in conjunction with a high contrast display, because a
log response will stretch virtually indistinguishable [by the human
vision] color differences in dark regions to rather large RGB
differences and will waste levels then (e.g. on display with a high, say
1:10000 contrast ratio, a log response will use 25% of the levels for
the 0.0001...0.001 intensity range, though this range corresponds only
to the 0.1%...1% range of the L* lightness).

But if for instance videos with a high dynamic range are displayed on a
high-contrast display in a dark environment, then a log response may
possibly indeed make sense. If for instance certain scenes in the video
are so dark, that the brightest areas in the scene are just say 1/100 of
the display's white luminance, then the vision certainly won't keep
adapted to display white in such a viewing environment, but will adapt
to the much lower luminance level of the scene, and then e.g. a regular
L* response [normalized to L* = 100 = display white] won't be
appropriate any more for this viewing condition.

Regards,
Gerhard

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