Newsgroups: sci.image.processing
Path: cantaloupe.srv.cs.cmu.edu!bb3.andrew.cmu.edu!nntp.sei.cmu.edu!fs7.ece.cmu.edu!hudson.lm.com!news.pop.psu.edu!news.cac.psu.edu!howland.reston.ans.net!pipex!bbc!alanr
From: alanr@rd.bbc.co.uk (Alan Roberts)
Subject: Re: Q: color difference: CIE vs. CMC
Message-ID: <D6GB5D.CM8@bbc.co.uk>
Sender: usenet@bbc.co.uk
Nntp-Posting-Host: sunf0.rd.bbc.co.uk
Organization: British Broadcasting Corporation, UK
X-Newsreader: TIN [version 1.2 PL0]
References: <3ledcs$17v@newsbf02.news.aol.com>
Date: Mon, 3 Apr 1995 08:48:49 GMT
Lines: 54

Hayworth (hayworth@aol.com) wrote:
: To color experts:
: I have a question about color difference measurement:

: I know that Delta E cmc is supposed to better mimic how humans perceive
: small color differences than is Delta E CIE (which = sqrt (delta L**2 +
: delta A**2 + delta B**2) = length of vector in CIELAB space), but I was
: wondering if the cmc formula is better for large color differences.  For
: example, let's say you are looking at color fading of samples.  Say a dark
: brown that fades to a light brown, and that white is your reference (100%
: faded).  We might find

: For Delta E CMC:
: Color diff(dark brown,  white) = 27
: Color diff(light brown, white) = 18

: but for Delta E CIE:
: Color diff(dark brown,  white) = 44
: Color diff(light brown, white) = 22

: Now, you could make the assertion that using the CMC formula, the sample
: faded 33.3% = (27-18)/27 (of the way towards white), but using the CIE
: formulas the sample faded 50% = (44-22)/44.  I don't know if you can say
: exactly which one is "right."  I was thinking of correlating this with
: human perception by running tests with dye solutions of different
: concentrations (e.g. using several samples of water with different numbers
: of drops of brown dye in them and seeing which one, 33% or 50% came
: closest).

: The papers on the subject all conclude that CMC is better, but were only
: validated/qualified for small color differences.  Has anyone looked into
: comparing the CIE and CMC versions of color differences versus human
: perception for large color differences?  What were your findings?

The textile industries in the UK developed CMC as a means of automating
the colour matching of fabrics. It was interested in purely automatic
measurement of differences between samples that the maunfacturers said
were identical, but which customers in the shops might not. As such, it
is a system for quantifying small differences only, and CMC is by far
that best system in common use.

There are no large-difference error spaces yet.

If you want more information on this topic you should consult Prof.
R.W.G.Hunt's latest book(s) on colour reproduction, where he goes into
great detail on the psycho-physics of colour recognition, and presents
a new model for the process. We are investigating that model now.

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