[argyllcms] Re: ColorMunki measurement drift

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 28 Sep 2010 13:58:57 +1000

Juergen Lilien wrote:

I asked, because in the Dispcal doc you only mention "Display white
level drift compensation" with the -Iw option, but not white point
compensation. I have to try it...

-Iw is specifically about trying to stop changes in display brightness
during measurement affect the calibration or profile. It certainly doesn't
attempt to second guess the instruments accuracy. So it won't have any
effect if the instruments absolute calibration were to drift.

As I said before, I wouldn't get too obsessed with white point errors,
especially when measured in degrees. It's visual difference that counts,
and that needs to be measured in delta E.

-Ib on the other hand, does compensate for instrument dark calibration
drift, on the assumption that the display black is largely independent
of any change in display brightness or other display variable.
Certainly on a CRT when there are no electrons hitting the phosphor,
this will be true. (It's not going to work so well on a CRT where there is
still phosphor emission for black though).
I guess an LCD pixel set to "off" will have a black that is somewhat
influenced by any backlight change, but the code attempts to allow
for this if both compensations are used (-Ibw). These sorts of
concerns are why I advised to use it if it improves things, and don't
use it doesn't.

Graeme Gill.

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