[argyllcms] Re: ColorMunki conforms to new XRGA Standard

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 24 Nov 2010 16:45:56 +1100

Juergen Lilien wrote:
XRGA conformity has an influence on the measured spectral data, so this
must also have an influence on the measured values obtained with the
combination ColorMunki+ArgyllCMS.

This should also mean that values measured with ArgyllCMS+ColorMunki are
not direct comparable with i1Pro+ArgyllCMS based values without applying
a correction matrix.

That makes various assumptions. X-Rites white paper is rather short
on technical details. For instance, there is no indication as to whether
future production of instruments are being calibrated to the XRGA standard,
or whether they are being calibrated to their historical standard,
with the drivers expected to apply a correction. The former would
cause a discontinuity in reading consistency between earlier and
later production units, while the latter leaves the choice of
standard in the hands of the user (ie. the use would be able
to select "historical" or "XRGA" readings from instruments, old or new.)
Their matrix corrections for historical data are called "proprietary",
hinting that they will not be published.

Given the lack of clarity and any detail in their announcement, I'm certainly
not going to do anything other than continue to use the calibrations that are
programmed into each instrument.

In practice: I measured the white balance patch of my newly acquired
ColorChecker Passport with the Argyll/ColorMunki combo and got different
values (Lab D50: 81.08_0.17_-0.03) compared to
Robin D.Myers technical report on the ColorCheckerP (81.34_-0.13_0.28).
But I know, the differences in measured values don't proof that XRGA is
the reason.

Nevertheless, do you still think, that's safe to directly compare
ColorMunki and i1Pro measured values when using ArgyllCMS?

"Safe" in what sense ? (I don't think the world will end if you
do such a comparison!). Intra and even inter instrument agreement
has always been a practical issue to one degree or another. If
color matching is critical to your application (ie. proofing),
the best advice is to always use the self same instrument for
all your measurements. If you can't do that, at least use the same
model and version of an instrument.

Graeme Gill.

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