[argyllcms] Re: Monitor calibration
- From: nome cognome <darkbasic4@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 23 Jul 2009 16:37:30 +0200
2009/7/23 Klaus Karcher <lists@xxxxxxxxxxxxxxxxx>:
> I guess the reason for this bad evaluation result is a white point issue.
> Probably Spectraview writes D50 as media white point to the profile, but
> Argyll expects the actual white point of the display (otherwise the white
> point tag is pretty useless and it is impossible to recover the actual
> colors from an ICC v2 display profile!).
You are right, I inspected the profiles and I saw Spectraview II
writes D50 while Argyll writes the monitor temperature (6900K with
hardware calibration only and 6600K with the software calibration
too). PCS is XYZ (they are all shaper/matrix profiles), so its white
point is 0.964, 1.000, 0.825.
Curve is 256-point for Argyll and gamma 2.2 for Spectraview II.
Despite that I think that Spectraview curve is sRGB instead of gamma
2.2. In such a case I should use -gs instead of -g2.2 in dispcal. This
should explain why I obtained worst results adding the software
calibration, am I right?
I made a screenshot of the curves:
http://darkbasic.homelinux.com/images/sv2/curves.jpg
Those are the profiles if you want to do some tests on them:
http://darkbasic.homelinux.com/images/sv2/profiles.zip
> The reason for this unfortunate
> situation is a arguable change (or "clarification") in the ICC profile spec
> regarding the media white point of monitor profiles (see below).
>
> Specification ICC.1:2004-10 (Profile version 4.2.0.0): "As specified in
> clause 9.2.25, for monitor profiles the mediaWhitePointTag shall be set to
> the PCS white point"
>
> <http://www.color.org/advantagesv4.pdf>: "An important consequence of this
> clarification is that Version 4 profiles for RGB displays and working spaces
> should only contain D50 tristimulus values in the media white point tag
> indicating the transformation to the PCS white point."
But those are ICCv4 specs while Spectraview profile is only v2.1!
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