[argyllcms] Re: ColorMunki measurement drift

Juergen Lilien wrote:
Actually I found the problem during the interactive calibration
of the monitor. 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 to push the monitor controls one more step, and so on.
I found that this iterative procedure takes more than 30min to

I think you are really aiming far too high. The general accuracy
and stability of these prosumer level instruments and displays
is simply not in that ballpark. 1 or 2 delta E is good. To get
into the sub 1 delta E region with any confidence, really demands
laboratory conditions, procedures, devices and instrumentation.

A major issue is positioning accuracy/device spatial consistency.
In reflective measurement for instance, it's easy to get
0.2 delta E simply due to a change in instrument position
on the substrate, even if it is very smooth and uniform.
I would expect that similar errors would be see on displays.
Eliminating this source of error requires locking the device
firmly in place, and often calibration requirements make this
impossible.

The expectation of 0.2 delta E tolerance for any specific
characteristic is questionable when the spatial variability of
the device is of a similar (or often greater) magnitude.

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?

I suspect this is a limitation of this level of instrument, particularly
with regard to emissive measurements. While reflective measurements
have an absolute calibration reference in the form of the calibration
tile, emissive measurements do not. To get beyond this really means using
a near laboratory grade instrument. Typically these are 10 times or more
the cost of the entry level spectrometers such as the ColorMunki
or EyeOne Pro.

Graeme Gill.

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