Color constancy and metamerism
Color constancy and metamerism
- Subject: Color constancy and metamerism
- From: "Mark Rice" <email@hidden>
- Date: Tue, 20 Sep 2005 12:25:36 -0400
Marco, I am no color scientist either, but I think you have it backwards
here. Color constancy is a characteristic of human beings, not of ink jet
prints. Color constancy means that our eyes and brain adjust to the existing
illumination to see whites as white, no matter what the surrounding
illumination (within reason). Ink jet prints cannot make this adjustment.
Metamerism means that two different sample areas on the ink jet print may
appear identical under one lighting condition, but appear different under a
different lighting condition. A classic example of this is my Epson 2200
simulating B&W prints - I have achieved near perfect neutral appearing
prints under 5000K lighting, but under cool white deluxe, the prints appear
slightly sepia. That is metamerism. Only an object can have metameric
qualities - human being cannot be metameric.
A classic reason for metamerism is this: take a single wavelength of light,
say 530 nm green and illuminate an object under it. Then take a series of
wavelengths (representing the spikiness that one often gets from fluorescent
illumination) that average out to equal 530 nm and illuminate the object.
Many object will appear to be different color under the different light
sources, although the color temperature and lighting "color" is the same.
Another classic metamerism example that many photographers have torn their
hair out over is this: an "olive green" dress will appear green to most
observers, but many times it will appear brown to many films (if anyone is
still using film). That's why us retouchers were invented!
Mark Rice
www.zero1inc.com
>From: Marco Ugolini <email@hidden>
>Subject: Metamerism vs Color Constancy
>To: ColorSync Users Mailing List <email@hidden>
>Message-ID: <BF54D55F.5428%email@hidden>
>Content-Type: text/plain; charset="US-ASCII"
>I premise this message by saying that I am NOT a color scientist (though I
>wish I was sharp enough to be one): just a guy who has been dabbling for a
>few years in matters that have scientific ramifications, which he is still
>trying to sort out for himself.
>So, there went the introduction.
>Now to what I wanted to ask: Metamerism vs Color Constancy.
>First, a definition of the terms (taken from the great web site
<http://www.answers.com <http://www.answers.com/> >):
------
>METAMERISM
>Metamerism is a psychophysical phenomenon commonly defined incompletely as
>"two samples which match when illuminated by a particular light source and
>then do not match when illuminated by a different light source."
>["Incomplete" because metamerism can also be subdivided into sample,
>observer, illuminant, and geometric metamerism]
------
>COLOR CONSTANCY:
>Color constancy is a feature of the human color-perception system which
>ensures that the perceived color of objects remains relatively constant
>under varying illumination conditions.
------
>I am bringing this up because my poor insufficiently scientifically-trained
>mind is trying to comprehend whether the term "metamerism" is currently
>being used improperly in color management circles.
>When we refer to inkjet prints as being "metameric" (a common buzzword
these
>days among the initiated to the growing sect of inkjet printing), do we
>actually mean, instead, that they lack color constancy?
>Metamerism happens between two samples (in sample metamerism, at least)
>whose colors have different spectra. This spectral difference creates a
>match under one illuminant (called a metameric MATCH) and a mismatch under
>another illuminant (a metameric FAILURE). I have been unable to retrieve
the
<etymology of the word "metameric," but it seems that it refers to parts
that
>appear or ought to appear similar if not identical to one another (as in
the
>segments of the body of an earthworm, which are called "metameres").
I>f that is so, then a print cannot, by itself, be metameric.
>So, if we use the word "metameric" to mean that a print changes its color
>appearance under different illuminants, shouldn't we actually say that IT
>LACKS COLOR CONSTANCY instead?
>Please tell me if I am wrong about this, but if I am correct could we
please
>stop saying that inkjet prints are metameric, then?
>Thank you.
--------------
>Marco Ugolini
>Mill Valley, CA
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