Re: Neutral grey under different lighting
Re: Neutral grey under different lighting
- Subject: Re: Neutral grey under different lighting
- From: Marco Ugolini <email@hidden>
- Date: Mon, 10 Sep 2007 08:54:23 -0700 (GMT-07:00)
Graeme Gill wrote:
>Incorrect. Illuminants are just sources of spectral radiation.
>If two light sources appear to be the same color but are composed
>of different spectrums, then they are a metameric pair.
That sounds like a stretch to me. There is CCT (Correlated Color Temperature, by virtue of which a light source is said to approximate a similar surface temperature of a Planckian blackbody radiator, though its spectral power distribution may differ) -- and there is metamerism. Are you saying that the very concept of CCT is itself a form of metamerism?
All definitions of metamerism that I have encountered in scientific literature so far have referred to the properties of two colored samples (*not* illuminants), and whether they match or not, be it due to properties of the illuminant or of the observer. Never have I read or heard of *illuminants per se* being considered metameric, if that is what you're saying.
But maybe you know something else that you haven't explained.
>You're leading yourselves right up the garden path in following the idea
>that metamerism is something intrinsically tied to reflective samples.
Frankly, I don't get your point, Graeme. How can it be just tied to the reflective sample? You need an observer, an *illuminant* and a sample (reflective or emissive -- if it's emissive, the illuminant is tied in with the sample, but can still be seen as an element in the mix). Tristimulus values are created by the interaction of the reflective sample's SPD with the illuminant and the observer's receptors. Clearly, there is no "intrinsic" anything in any of this.
Marco Ugolini
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