[argyllcms] Noticeable differences between calibrated white points
- From: János, Tóth F. <janos666@xxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 26 Oct 2010 01:23:43 +0200
Well. This is not a part of my job, I only do this calibration thing as a
hobby (a supplementary for my hobby, like home cinema). So, my goal is the
adequate viewing experience, not some kind of hard correspondence for
standards.
But I have two displays right now. I placed them next to each others (I
power up the secondary when I need more place for my CAD drawings and other
documents at the same time --- for example, a standard in A4 paper format
and a Mathcad window to see what should I draw...).
The main display is a H-IPS and the secondary is an S-PVA. The first one is
a 10 bit display but the VGA card is able to do some dithering on the LUT
output, so I can calibrate it with effectively 10 bit precision. I think it
should be enough for "something".
The instrument is a ColorMunki and I use it in Adaptive HiRes mode (but I
tried the normal HiRes mode as well - it kills the shadow detail but I want
to talk about something else here...) and I use the Black/White measurement
drift features during the High quality calibration (in ArgyllCMS/dispcal, of
course :)
They always showed different colors because the H-IPS has a very wide gamut
(but I mostly use it in hardware emulated sRGB mode) and the S-PVA has a
near-AdobeRGB gamut. So, it's obvious that they should show different colors
when I don't do any gamut conversion with softwares (and the purpose of the
secondary display is mostly black and white document viewing, so...) and
even if I do, the S-PVA can't cover the full sRGB or AdobeRGB gamuts while
the H-IPS has a ~100% coverage. So, I never expected that they will show the
same colors.
BUT I expected that they will show the same white after a fresh calibration.
But no...
I watched black and white documents on both of them at the same time and I
noticed that they show very different whites. So, I thought I should
recalibrate them. But it didn't help.
The measured dE2k error was 0.3 and 0.0 dE2k after the calibrations. My
instrument used to be in the dE2k 0.3 range between continuous measurement,
so the highest possible dE2k should be under 0.9 (at max ; relatively, I
don't speak about the absolute error...).
But they shows noticeably different whites!
I also tried to measure these numbers with a "cross-acclimatized" instrument
(I re-checked the first display after I finished the calibration on the
second display). There were no any significant difference (it was a luck but
it read the exact same dE=0.0 on the H-IPS).
I invoked an EIZO document where they stated that you need FOV10 observer
for color matching displays.
OK, I used the FOV10 observer (and the correct x;y coordinates but it
doesn't really matter when we talk about relative differences).
The only difference that both displays have a reddish tint now. And the
relative difference is equal, or may be higher (but not smaller at all).
Now what?
The instrument usually does a good job until you don't have two displays
next to each others to judge. If the uncalibrated display feels
bluish/reddish/greenish, then the calibrated state will feel as "white".
Is it normal? Or is my instrument broken or is it unable to calibrate the
WCG display, or what...?
I don't know if it can make a significant difference in the perception of
the white color when it's filtered and mixed from different spectrums. Is
it? (Sorry, if this whole email was a noob question.)
I made these pictures with a smartphone, so you should ignore those
horizontal and vertical lines. I wanted to catch the relative differences,
not judge about "which one is whiter":
http://img12.tar.hu/janos666/img/92530301.jpg
http://img12.tar.hu/janos666/img/92530300.jpg
http://img12.tar.hu/janos666/img/92530302.jpg
And here is the difference between the FOV10 calibrated states:
http://img12.tar.hu/janos666/img/92530754.jpg
http://img12.tar.hu/janos666/img/92530753.jpg
(Cheap camera, etc. - they were both reddish a bit, so don't mix the
pictures! But it shows that the relative difference is even bigger.)
And I accidentally discovered something when I watched these white screens.
This is the display of my pocket-calculator:
http://img12.tar.hu/janos666/img/92530303.jpg
http://img12.tar.hu/janos666/img/92530304.jpg
When it reflects back the white light of the H-IPS WCG display, I can only
see a deep purple display (cheap camera again... And I think the color I see
is out of the sRGB gamut. So, it's blue here...) I can't read any numbers on
it.
When I use the white light from the S-PVA display, I can easily read the
displayed numbers. There is no any colorization. It's like the sunlight.
It's strange and funny for me but does it means anything for you? :)
(Has it anything to do with the relative subjective differences?)
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