From: dannyrich@aol.com (DannyRich)
Subject: Re: are black and white colors ? if yes, why ?
Date: 17 Dec 1999 00:00:00 GMT
Message-ID: <19991216225741.18706.00001188@ng-cm1.aol.com>
References: <38558b7c_2@newsread3.dircon.co.uk>
Organization: AOL http://www.aol.com
Newsgroups: sci.engr.color
X-Admin: news@aol.com

>I'ld like to think that the notional response of the 'standard eye' was
>derived from quite a large sample. And most people, with classifiably normal
>colour vision, do come pretty close. But not all.

The 1964 (ten degree field) observer had about 50 observers but the 1931 (two
degree field) only had about a dozen.  The 1964 work included a few foreign
post-doctoral fellows but the early work included only Englishmen from the
region near to London.

Since absolute spectroradiometry was not yet invented, the early work need a
normalization constant.  They used the reflectance of a white glass tile from
the NPL.  The range of matches to the white of that tile by about 40 observers,
all classified by the NPL as color normal, spanned about 50 CIELAB color
difference units (at the white point CIELAB and the MacAdam  1 std. dev.
ellipsoid are approximately equal).

  >The colour matches are not done to >monochromatic light. I may be out of
date
>here, but they were always done to red, >green and blue, with the facility to
>ADD known quantities of the primaries >to the unknown to allow for the
negative >numbers required to get the full >spectrum locus, on a RGB diagram.

The study by Guild was done with RGB filters but WDWright built the first
trichromator and used 435.8nm (blue), 546.1nm (green) and 650nm (red).  He
transformed Guilds broad band stimuli into a standard set of monochromatic
stimuli before averaging them together to for the CIE 1931 color matching
functions.


DannyRich@aol.com