[argyllcms] ColorMunki measurement drift

  • From: Juergen Lilien <jp.lilien@xxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 26 Sep 2010 04:05:36 +0200

Hello everyone,

I am still researching why it is very difficult to get repeatable
(stable) measurements with my ColorMunki, and why the measured
white point seems often to be off several hundred Kelvin, compared
to my manufacturer pre-calibrated monitor (NEC PA series).

In a first try I attached the ColorMunki to the screen and let it take
more than 1200 white point measurements (hires adaptive mode) in a row,
this took roughly an hour. At this time the monitor was several hours
in on state, so it should be pretty stable.

Please have a look at the attached graphs (each measurement is a point),
the complete "-d6" logfile is available on request.

The measured luminance was, after a very short stable beginning,
constantly decreasing (from about 133 to 130 cd/m²) with no stable
endpoint in sight.

The color (X/Y) measurements are even more interesting, they are
also decreasing but the variance is not constant, there are knots
in the point graphs with less variance and the period between the
knots is increasing over time - the pattern is more stretched.
At the end the measurements seem to have reached a semi constant
state with nearly no further decreasing tendency.

My first thought was to wait an hour with the ColorMunki on the
screen, until the color measurements reach the stable bottom,
before starting calibration and profiling. The problem is, that
the first (highest) readings seem a lot more reasonable compared
to my pre-calibrated monitor presets, and even after a self-
calibration of the ColorMunki they never get back to the start
level. Yes, this effect (temperature drift?) seems to be at
least partly immune against self-calibration of the instrument!

To prove this I started a second series of measurements with a
self-calibration after each single measurement and I still see
decreasing luminance and X/Y color values.

To be honest, I'm lost at the moment...

What is your ColorMunki operating experience?
Is my ColorMunki broken?

Should I reinstall the X-Rite software and check if I see the
same decreasing measurement values?

And what is the practical relevance? The DE of the first
measurement was 2,6 and it dropped to 0,7 at the end,
a 1,9 DE white point difference should be visible(?).

As I understand the new -I option will only help to counteract
drifting in the brightness level measurements, but does not
help with the color/white point drift?

You see, any input is greatly appreciated! ;-)

Best regards, Juergen

Attachment: ColorMunki_HiresAdaptive_60min_Graph.gif
Description: GIF image

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