Re: Ooops - D65 != D65 ???
Re: Ooops - D65 != D65 ???
- Subject: Re: Ooops - D65 != D65 ???
- From: Uli Zappe <email@hidden>
- Date: Tue, 19 Jun 2007 00:06:33 +0200
Am 18.06.2007 um 23:20 schrieb Robin Myers:
D65 is standardized and unambiguous. Tristimulus values of X 95.04,
Y 100.00, Z 108.89, chromaticity coordinates of x 0.3127, y 0.3290.
OK, good to know. So in theory, D65 == D65 ...
You are probably encountering measurement error between the devices.
I performed a lot of test measurements, each device at least 3 times
with each setting. While there may be slightly different values
within the various measurements with one device, these differences
are a far cry from the drastic differences between what an Eye-One
Display, an Eye-One Pro, a huey Pro and a ColorVision Spyder regard
as D65 (the Eye-One Display and the Eye-One Pro even while using the
same software!)
So basically every device is consistent to itself, none to the other
(even using the same software as in the case of Eye-One). So far, I
have tested 4 devices. If I had just bad luck and the differences
stemmed from faulty devices, this would mean that 3 of the 4 devices
(all sent to me directly from the manufacturers for testing purposes)
were faulty - that's highly improbable.
So I'm at a loss as to what kind of measurement errors I would
experience; it surely looks like a systemic error.
If you are measuring fluorescent illuminated LCD displays, there
are more variables that can influence the measurement. For
instance, the amount of time warming up the display, whether the
LCD is in a laptop or a desktop display, the ambient temperature,
room illumination levels and color, etc.
All the measurements took place under conditions as similar as
possible, so I'm sure that's not the reason, either.
One additional remark: I was amazed that even in the expensive Eye-
One Pro package, the software is nothing more than a black box
that somehow produces a profile. There's no way to access the and
work with the physical measurement data at all. Is this generally
the case with this kind of products (well, AFAIK there aren't many
alternatives to an Eye-One Pro XT package, anyway), a kind of
"people in the graphics industry are no scientists" syndrom?
(That's really a difference to the music industry, BTW. When you
buy a package to calibrate a loudspeaker, you'll have access to
the basic physics of the process as much as you want.) Is there
third party software to fill this (expensive) void? So far, I
stumbled across SpectraShop and BabelColors, but hadn't time yet
to look if they really do this kind of thing.
As for modifying the physics of the spectrometer, very few
instruments allow this.
I was not talking about modifying the measurement device, just about
getting access to the physical measurement results and the ability to
tweak them for testing purposes.
Speaking for SpectraShop, it can take in data from an i1 and let
you work with it in many ways.
I'll certainly have a look as soon as I find time.
But it gets weirder still: today, I got a ColorVision SpyderPro
which, just like the Eye-One Pro, allows to set the whitepoint in
xy coordinates. So I produced profiles with both devices using
x=0.311 y=0.344 (which equals 6503 Kelvin). All other settings
were as identical as possible. You can't get any more precise than
that, and still, the whitepoints differ a lot. This is absurd!
It may not be the white point but the neutral scale which is off. I
have seen many profiles produce an "off color" image because
various portions of the neutral tone scale were not achromatic.
Now my lack of knowledge begins to show: so far, I'm really only
talking about the display of white as in RGB 255-255-255, not about
the display of actual images. Can the neutral scale influence the
display of white?
X-Rite (the new GretagMacbeth/X-Rite merged company) may be using
an older ICC definition (v2 profile). The v4 profile definition has
not been incorporated into all the shipping products. So the new
definition may have explicitly defined the use for the "lumi" tag
where the previous version left it ambiguous.
Well, as I found out and quoted in my last post, neither X-Rite nor
ColorVision do the "right thing" according to the current
specification. Just what the right thing (for storing the whitepoint)
would be, remains a mystery to me ...
You should also check out ColorThink from Chromix.com . It might
help you.
Thanks for the hint!
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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