Re: Ooops - D65 != D65 ???
Re: Ooops - D65 != D65 ???
- Subject: Re: Ooops - D65 != D65 ???
- From: Uli Zappe <email@hidden>
- Date: Wed, 20 Jun 2007 20:07:22 +0200
Am 20.06.2007 um 18:37 schrieb Robin Myers:
You are confusing "repeatability" with "inter-instrument agreement".
I was aware of the difference, but not of the English terminology
used in this context, so thanks for clarifying this.
Looking at the error in your measurements we have:
x y dx dy
D65 Target 0.313 0.329
i1 Display 0.315 0.341 +0.002 +0.012
i1 Pro 0.314 0.333 +0.001 +0.004
Huey 0.307 0.328 -0.006 -0.001
Spyder2Pro 0.313 0.325 0.000 -0.004
The dx and dy values are the differences in the x and y coordinates
from the reference D65 values.
As you can see, the i1 Pro and the Spyder2Pro show almost the same
error and they were the best of the test.
Yep.
The questions raised by these measurements is how they were
sampled? Were they single measurements? Were they multiple
measurements and averaged? If averaged, how many measurements?
I performed at least 3 tests for each device and setting, but since
the repeatability was very high (never more than 0.002 variance), I
simply posted "typical" results and not actual averages. They really
wouldn't show much difference, though.
What was the ambient temperature?
About 26ºC (79º F), which is as cool as it currently gets at night in
Germany ;-)
The warm-up time?
The monitor had run more than 12 hours before.
Were the measurements made in exactly the same place on the screen?
Yes.
Was the instrument in the exact same orientation (LCD screens emit
polarized light which effects the measurements differently for each
type of measuring device as shown in the following report:
http://www.rmimaging.com/information/lcd_spectro.html
Interesting. This could have varied, because I didn't take care of
it. Still, because repeatability was so high compared to inter-
instrument agreement (and I did *not* perform the 3 measurements for
one device directly one after another), I still think that the above
differences mostly don't stem from different measurement conditions.
As you are discovering, measuring emissive displays in ways that
remove the variables and allow true comparisons between instruments
is a very difficult task.
Yep ;-)
I also performed tests with a "native whitepoint" setting (apart
from the huey, which does not have such a setting), which at that
time Spyder's Info window reported to be 0.311 / 0.338
Eye-One Display: 0.309 0.337
Eye-One Pro: 0.310 0.337
Spyder2Pro: 0.310 0.337
So here the results are basically consistent. I still don't know
enough about all this, but I *assume* that a "native whitepoint"
setting basically just means *omitting* a calibration step, and if
the issue happens during this step, it's clear why this setting
will work. :-)
Since the instruments are agreeing with each other with respect to
the native white point measurement, other places to look for the
error in your D65 settings are in the various software packages,
I'm specifically interested in what you say here. This sounds as if
using a native white point setting does *not* simply omit an
otherwise failure-prone step, but *does* perform a respective
measurement, and one that works very consistently, at that, between
the different devices. Is this correct? If so, this would suggest
that the differences are not primarily caused by shortcomings of the
devices, but rather by the software handling the data (although in
the case of the 2 Eye-Ones, the only explanation for their different
results with seemingly the same software would be a different
handling of colorimeter and spectrophotometer data on Eye-One Match's
side).
the video card's ability to achieve a particular white point and
the monitor's ability to produce the requested white point.
But if the monitor can achieve the whitepoint with one software, why
shouldn't it with the other?
I have a gut feeling that it's the software (just think of the Spyder
producing different results with v4 ICC profiles), but of course,
what do I know? ;-)
Bye
Uli
________________________________________________________
Uli Zappe, Solmsstraße 5, D-65189 Wiesbaden, Germany
http://www.ritual.org
Fon: +49-700-ULIZAPPE
Fax: +49-700-ZAPPEFAX
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