Re: On ICC Relative Colorimetry
Re: On ICC Relative Colorimetry
- Subject: Re: On ICC Relative Colorimetry
- From: Phil Green <email@hidden>
- Date: Thu, 27 Sep 2001 23:11:28 +0100
- Organization: LCP
Roger Breton wrote:
>
How is it possible to "decouple" the Illuminant of a Standard CIE
>
Colorimetric measurement and instead make that measurement "relative" to the
>
paper?
You're mixing two things up here.
A measurement is always made with a given illuminant, which should
correspond closely to the condition of viewing. If you want to compute
new coordinates for a different condition of viewing, it's best to go
back to the spectral data and substitute the new illuminant data in the
calculation of XYZ, but if you don't have the spectral data then you can
do a chromatic adaptation transform (e.g. Bradford) to approximate the
result.
The issue of 'relative' vs 'absolute' colorimetry is just to do with how
the XYZ data are normalised when calculating CIELAB coordinates. You can
go back and forth between different normalisations (i.e. different
reference whites) without ever changing the illuminant.
--
Phil Green
Colour Imaging Group
School of Printing and Publishing
LCP
Elephant and Castle, London SE1 6SB
Tel: +44 020 7514 6759 Fax: +44 020 7514 6772
http://www.digitalcolour.org