Re: Questions on some basic definitions and concepts.
Re: Questions on some basic definitions and concepts.
- Subject: Re: Questions on some basic definitions and concepts.
- From: Andrew Rodney <email@hidden>
- Date: Mon, 10 Mar 2014 08:51:23 -0600
On Mar 10, 2014, at 8:43 AM, Andrew Rodney <email@hidden> wrote:
> I've got an email from this list a few years back specifying the various locations and I'll see if I can dig it up. But the idea it's one measurement taken in one location at one time doesn't seem correct.
Check the archives for a topic called: The history of Standard Illuminants, June 2011. Posted by John (No last name), it was quite interesting. A portion of what John wrote is below:
> The series of D-illuminants was adopted by the CIE in 1971 based on 622
> measurements from the early 1960s: 249 at Rochester, NY (Kodak); 274 at
> Enfield, England (Thorn Electrical Industries); and 99 at Ottawa, Canada
> (National Research Council). Each of these labs contributed spectral
> measurements taken with different kinds of instruments measuring at
> different spectral intervals over slightly different ranges. The data
> were combined into a master set consisting of averages over 10 nm
> intervals from 330 to 700 nm from which the average and four
> characteristic vectors were calculated. The average and first two of
> these vectors account for most of the variance in the observed data and
> live on as the S0, S1, and S2 vectors used to calculate the
> D-illuminants in the CIE standard (see Wyszecki & Stiles, 2nd. Ed., page
> 146). S0 is the mean, S1 provides a yellow-blue variation relating to
> cloud cover and inclusion/exclusion of direct sunlight, and S2 provides
> a pink-green variation which was thought at the time to derive from
> variations in atmospheric water vapor and haze.
>
> All of this was reported by Judd, MacAdam and Wyszecki, J. Opt. Soc.
> Am., Vol. 54, p. 1031 (1964) and was incorporated without change into
> the 1971 CIE standard except for the addition of the formula for
> illuminant chromaticities in terms of correlated color temperature due
> to Kelly at NBS (now NIST, Washington, D.C.).
Andrew Rodney
http://www.digitaldog.net/
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