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List:       kde-kimageshop
Subject:    Re: New reason for XYZ
From:       Kai-Uwe Behrmann <ku.b () gmx ! de>
Date:       2007-03-07 11:40:46
Message-ID: Pine.LNX.4.61.0703071334340.7080 () sirius ! rasena
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Am 07.03.07, 12:15 +0100 schrieb Cyrille Berger:

> > The difficulty arrises by the usable points in the conversion LUT. As XYZ
> > is very huge, the used point in the transforming LUT to tell about the
> > right transistion are a few only. With fewer points less accuracy ...
> >
> > To visualise look at the devicelink tables in ICC Examin.
> Hum, but isn't XYZ use as a PCS ? I mean when doing color transformation, 
> don't we do something like RGB -> XYZ -> ( eventually LAB) -> something 
> else ? So RGB -> XYZ -> RGB should return the same value, or have I missed 
> something (which is surely the case ;) ) ?

RGB -> XYZ LUT profile are rare. XYZ matrix ones can be precalculated in 
floating point precision. The final device link used by lcms for the 
colour transformation is RGB -> RGB. 
The imprecision with 8- and 16-bit starts where one have to do a 
deviceRGB/CMYK <-> XYZ conversion with a LUT involved.

regards
Kai-Uwe Behrmann
--
development for color management 
www.behrmann.name + www.oyranos.org + www.cinepaint.org

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