[argyllcms] Re: Measuring a colorcheker on screen

Am 22.01.08, 23:27 +0100 schrieb Lars Tore Gustavsen:

> I found an old Seybold Report with the title "Measuring the quality of
> ICC profiles" 
> http://www.heidelberg.com/wwwbinaries/bin/files/dotcom/en/prinect/prinect_profile_toolbox.pdf
>  . On monitor profiles they have three objective test for the quality.
> The are, page 13, archived gamma, DE difference in whitepoint from
> target D50 and the last one average DE for a colorcheker measured on
> monitor.
> 
> I tried to do the last step. I found a digital LAB version of the
> colorchecker 
> http://www.colorremedies.com/realworldcolor/downloads/Macbeth_ColorChecker_LAB.tif.zip
> I fixed? (added a white patch nr 25) to the colorcheker.ti2 in the ref
> directory(attached), and measured the colorchecker when I viewed it
> with cinepaint with colormanagment on. I then measured it with
> "chartread -d -H  ColorChecker" with my eye-one pro.

The display in CinePaint, even with the ICC absolute rendering intent, is 
not CIE absolute. The later would be in need to do a real light 
comparision. You measurings are in need to scale up or down to match the 
monitors white- and blackpoint.

You need to know about your monitors black and white point. 
The measurement tag included in some profiles is the only easy to check 
way to make assumptions about the real gamut of a emissive device through 
a profile.
All other tags in a profile to describe the monitor ligthness are eigther 
non existent in real profiles or possibly wrong. I found only a few 
profiles which allow for assumtions about the real world device gamut. 
A warning, as soon as the monitors whitepoint is measured around Y 100 in 
the profile included measurement tag, you can discard the whole tag
as it is very likely as values where prescaled to the ICC range.

A option in Argyll to include the measurements would help in later veryfy 
the profile by external tools as what Lars did want to achieve. 
LProf does the measurement embedding already, at least on request.

Does Argyll support CIE absolute calculations?

kind regards
Kai-Uwe Behrmann
--
developing for colour management 
www.behrmann.name + www.oyranos.org

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