RE: Metamerism and Color Constancy
RE: Metamerism and Color Constancy
- Subject: RE: Metamerism and Color Constancy
- From: "Peter MacLeod" <email@hidden>
- Date: Tue, 4 Sep 2007 09:26:28 -0700
- Thread-topic: Metamerism and Color Constancy
> Here is another one of my periodical reminders:
>
> *Metamerism* is the effect whereby *two* colored objects
> built with colorants of different spectra appear to match one
> another colorimetrically under a given illuminant. It's a
> *positive* effect, not one that should be avoided. Without
> metamerism, the only way to match a target color would be to
> create it with exactly the same pigments and materials.
>
> On the other hand, the phenomenon whereby a colored object
> changes appearance under different illuminants is called
> *color inconstancy*.
>
> This distinction may seems like nitpicking to some, given how
> used we have become to hearing "metamerism" used in place of
> "color inconstancy" even from people who ought to know better
> -- but it's not, since the two expressions actually indicate
> two sharply distinct phenomena.
>
I think you have to be careful here. Metamerism, whether caused by a
change in illuminant or by two different samples under the same
illuminant, is a color match that happens because the integration of the
spectra with the color matching functions yields identical tristimulus
values. In the case of illuminants it's called "illuminant metamerism"
in much of the literature. For example, you could think about a very
spiky fluorescent light that matches a particular color sample against
how that same sample looks under real D65 (think of a split-field
apparatus like the ones used in the standard color matching experiments,
where the two sides have an identical sample but different illuminants),
but not all color samples, in which case the colors that matched were
cases of illuminant metamerism, while the colors that didn't match
represent illuminant metameric failure. That's not the same thing as
color constancy. The "Metamerism (color)" wikipedia page describes this
pretty well: "Color constancy is the everyday perception that the color
of objects remain unchanged across significant changes in illumination
color and luminance level. Color constancy is related to memory colors
and discounting the illuminant."
--Peter
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