Subject: Re: Color (colour)

From: [email-masked] (William Dawes)
Date: 11 Aug 1995 03:30:29 GMT

In article <[email-masked]>, [email-masked] says...
>
>Color (Colour) measurement and tolerancing!
>
>I am seeking information about a color tolerancing system called CMC.
>
>It uses L, c, h color space and establishes ellipsoid tolerances around targets. Ellipsoids get
>larger with higher chroma values simulating human sensitivity.

	Well, of course all color metrics have claimed that they
	simulate human sensitivity. Macadam (from P.G.Nutting's
	observations) established ellipses first, maybe 40 years
	ago. The FMC units were the first practical applications
	of theses when computers became available...

>
>This system is extensively used in the U.K. and E.C. for establishing color specifications (colour
>specifications).  It was developed for textiles and dyes.  It is an ISO standard and mimicked by
>AATCC standards.

	Oh? I thought the AATCC was exactly the same as CMC???

>If you use this system or know where I can talk with someone who does, please drop me a line
>at [email-masked]

	The CMC system is enjoying widespread use here in the US
	now. Though it was develped by McDonald at Coates using
	threads, and has been adopted by the AATCC here, it is
	also used widely in the plastics industry. When using the
	L:C ratio of 1.3:1, it has been shown to correlate much
	better with visual pass-fail judgements than CIELab 1972 or
	1994, McAdam, or Hunter Lab. (SPE ANTEC, 1995, Mulholland)

	I believe the CMC metric is currently an option on all new
	color measuring equipment. I know Eastman plastics, Hoechst-
	Celanese, and Allied-Signal use it, and I believe Ford
	requires it.

	Often the CIE L, a, and b values are also used by colorists
	used to thinking in red-green and yellow-blue terms, especially
	in the gray and near neutral colors, where they just make more
	sense than dHue and dChroma.

	Just what do you need? I have QuickBasic code that calculates
	it from tristimulus values, if you want to add it to some
	existing software of yours... will be happy to talk to you
	on the phone, or put you in touch with experts who have
	thouroughly evaluated it in plastics.

	Bill

-- 
--Bill Dawes          <[email-masked]>      804 748-8639--
--http://www.infi.net/~wmdawes/ Personal pages
--http://www.infi.net/~color/   Home of the COLORING pages--

---

From: [email-masked]
Date: Mon, 14 Aug 1995 20:47:48 GMT

>If you use this system or know where I can talk with someone who does, please drop me a line

You might want to contact Minolta Corporation at Ramsey for more
information.  They manufacture a range of color instrumentation.
Hope this help.

GT