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From: alanr@rd.bbc.co.uk (Alan Roberts)
Subject: Re: FAQ purpose/colorspace-faq
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Date: Fri, 12 May 1995 12:44:37 GMT
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Xref: glinda.oz.cs.cmu.edu comp.graphics:76407 sci.image.processing:14570

Alain:

Ok, I give in. I will only use "linear transformation" when implying
matrix multiplication. Chromaticity coordinates do indeed have a non-
linear relationship with the tristimuli through normalisation, and I
should not have implied that that was a linear transformation.

Chromaticity coordinates are "directly related" to tristimuli, not
"linearly related".

: Now what ? IMO, the expression 'linear transformation' should only be
: used when speaking about a true linear transformation (matrix mult),
: or anyone with a little math background will get shocked. In the Poynton
: FAQs, I did not find any incorrect use of the word, another proof that
: they are really very, very well thought out. I don't know how one can
: qualify things like Yxy in colorimetry, to properly say that 'they are
: _as_a_set_ related directly to linear light', but calling them the 
: result of a linear transformation is to be avoided.   

--
************* Alan Roberts **************
* BBC Research & Development Department *
* My views, not necessarily Auntie's    *
*    but they might be, you never know. *
*****************************************
