[argyllcms] Re: ColorMunki measurement drift

  • From: Roger Breton <graxx@xxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 26 Sep 2010 13:54:26 -0400

Hallo Jurgen,

I have both a ColorMunki and an EyeOnePro here. Maybe you can guide me in
some comparative testing for you? I'm kind of busy these days but I can give
it a try...

BTW, I am no video engineer but, sometimes, I wonder to what extent is the
110V/220V input voltage fluctuation could influence the monitor emitted
light? Crazy idea, I know.

First reading, you say, was "White level = 156.70 cd/m^2" + "6610K".

After 19 consecutive readings, you say you get "White level = 152.46 cd/m^2"
+ "6958K".

The Luminance drop is only 3%, which is not so bad. But I agree the CCT
shift of +348K is troubling?

Black level going up, anything below 1 cd/m2 measured with these
"affordable" instruments (i1pro, Munki, DTP92), is to be taken with a grain
of salt, IMO. These instruments are never sensitive enough to measure such
low light levels with any precision or accuracy. 

I would like to try to replicate your findings, if I could? You may have a
slightly "defective" ColorMunki, unless they all measure with that kind of
precision. Which I'm not sure. 

MfG / Roger

> -----Original Message-----
> From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-
> bounce@xxxxxxxxxxxxx] On Behalf Of Juergen Lilien
> Sent: 26 septembre 2010 11:19
> To: argyllcms@xxxxxxxxxxxxx
> Subject: [argyllcms] Re: ColorMunki measurement drift
> Roger Breton wrote:
> Hello Roger!
> > I wish you had an EyeOnePro to compare, ...
> Yeah, that's my wish too. ;-)
> > ...because, to my knowledge, EyeOnePros are not susceptible to the
> > effects you describe (if EyeOnePro drifted as much as you report, I
> > would start to worry).
> I started with a Spyder2 years ago, but the results were not to my
> satisfaction, so I thought to make a big step forward with the ColorMunki,
> only to find there is still something fishy with my instrument readings.
> It would be really interesting to compare with an EyeOnePro, but I've read
> recommendation to sent an EyeOnePro once a year to the manufacturer for
> recalibration, so I would expect that inter instrument agreement is not
> without problems, especially between different types of instruments (e.g.
> EyeOnePro and ColorMunki).
> Of cause, I would by happy with my ColorMunki to get very similar results
> with two measurements being 30min apart.
> > Do you leave the ColorMunki hung to the screen for an hour before
> > making your measurements? To try minimizing thermochromism effects?
> > It should help, in my opinion.
> Actually I found the problem during the interactive calibration of the
> It is really a hunt to set the white point within
> <0,2 DE. After several readings the DE starts to increase again, so I have
> push the monitor controls one more step, and so on.
> I found that this iterative procedure takes more than 30min to get in the
> region of more stable readings, that actually result in better looking LUT
> curves. So yes, recently I leave the ColorMunki roughly an hour on the
> (measuring the white point) before I start over with the real
> calibration/profilation.
> But the problem remains, that the agreement between monitor (preset) and
> ColorMunki constantly degrades after the first reading (without
> acclimatization time) even with self-calibration.
> E.g. monitor preset is 6500K (Blackbody):
> First measurement of uncalibrated response with "cold" ColorMunki:
> Black level = 0.22 cd/m^2
> White level = 156.70 cd/m^2
> Aprox. gamma = 2.19
> Contrast ratio = 721:1
> White chromaticity coordinates 0.3115, 0.3242
> White    Correlated Color Temperature = 6610K, DE 2K to locus =  2.1
> White Correlated Daylight Temperature = 6612K, DE 2K to locus =  2.8
> White        Visual Color Temperature = 6534K, DE 2K to locus =  2.0
> White     Visual Daylight Temperature = 6720K, DE 2K to locus =  2.7
> This looks quite reasonable, but 19 consecutive measurements
> _with_prior_self-calibration_ later I get this:
> Black level = 0.24 cd/m^2
> White level = 152.46 cd/m^2
> Aprox. gamma = 2.17
> Contrast ratio = 642:1
> White chromaticity coordinates 0.3064, 0.3196
> White    Correlated Color Temperature = 6958K, DE 2K to locus =  2.4
> White Correlated Daylight Temperature = 6960K, DE 2K to locus =  2.4
> White        Visual Color Temperature = 6854K, DE 2K to locus =  2.3
> White     Visual Daylight Temperature = 7065K, DE 2K to locus =  2.3
> Despite the self-calibration the black level is up, white level + gamma (+
> contrast ratio) are all down and the white point has changed about nearly
> 350K in the wrong direction.
> What's going on here?
> Best regards, Juergen

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