[argyllcms] Re: Strange contrast clipping during calibration

  • From: János, Tóth F. <janos666@xxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 21 Aug 2012 04:32:52 +0200

Hmm. I always used ~0 and ~200 black and white targets for every devices
with higher native black and lower peak white luminances. It never caused a
problem like this (nor any other error I noticed).
I actually thought it's better to set up the parameters like this, so
dispcal won't lift up the black level in case the random measurement error
caused a slightly too high black level reading when dispcal establish the
"native black level" (and the same for th other end of the scale in inverse
with similar small dynamic range clipping).
Good to know it's bad idea.

It's CCFL but I don't think the brightness drifts that much. It was
properly warmed up. And I left the i1d3 on it for ~10 minutes measuring the
white point before I started the calibration (it's not as hot as the
desktop monitors, but I had the time, so let it acclimatize...) and the
white luminance didn't change too much (otherwise I would have gotten
scared about the hardware and/or tried to adjust the luminance back to the
desired point).

This is an old laptop and it was calibrated a few times before. I just
wanted to re-calibrate it (the last calibration was about 6 months ago).
The contrast wasn't clipped like this before. But now, I repeated the
calibration twice (with slightly different settings, like gamma 2.2 instead
of 2.35) and I always got a clipped LUT like this.

I will give it a try with "native" black and white luminance settings

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