Thread-topic: filmscanners: metamerism and Epson 2000P
I think the definition you are quoting is just incomplete, and confusing
as a result.
All it talks about is the fact that some object "look" the same under
some conditions (even though their spectral response is different). The
corollary (which is not included in the section you quote) is that under
*other* conditions, the two objects will *not* look the same.
Here are some other definitions, all of which agree with the definition
provided at
1) from:
Colour Science Glossary
Metameric Colour Samples (Metamer)
A pair of colours which differ spectrally but which yield the same or
similar tristimulus values under at least one set of viewing conditions.
Metamerism
A metamer which match each other under one set of conditions but
mismatch when viewed under another.
2) from:
Metamerism
Daylight Tungsten
Two samples of textiles that match under one light but not under another
one called a matameric pair
The colour of a fabric can match that of another under one light but not
under another. On the left are two green samples seen under daylight. On
the right the same two samples are completely different under another
light such as tungsten. This illusion can cost a client a lot of money
if the colours haven't been checked under both lights. This is because
the two samples are from different batches of the 'same colour' dyed
with completely different chemicals.
3) from
Metamerism - Terminology and Definitions
Metamerism always involves a pair of objects. The two objects can be
described as "metameric objects", or a "metameric pair". They are
sometimes said to be "metameric", "exhibit metamerism", and/or be
"metameric matches".
Metameric Objects exhibit the following:
They have different spectral reflectance factors (spectral curves).
They match under at least one combination of illuminant and observer.
They do not match under at least one combination of illuminant and
observer.
4) from
Metamerism:
Two colored objects made from two different dyes or pigments may look
the same under one light source, but different under another light
source. This is what is known as metamerism. Two different colors may
appear to be exactly matched simply because the combination of spectral
reflectance and source distribution is fortuitously matched! However,
this pair will not be a perfect color match when viewed with another
light source. The combination of spectral reflectance with the spectral
distribution of the second light source will be different, thus the
colors will be perceived as mismatched. The pair of colors are said to
exhibit metamerism. Pairs of colored objects having the same spectral
reflectance curves and therefore the same color perception for all light
sources are nonmetameric and form an invariant pair.
-----Original Message-----
From: Frank Paris [mailto:marshalt@spiritone.com]
Sent: Sunday, January 28, 2001 11:20 PM
To: filmscanners@halftone.co.uk
Subject: RE: filmscanners: metamerism and Epson 2000P
> -----Original Message-----
> From: owner-filmscanners@halftone.co.uk
> [mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Eli Bowen
> Sent: Tuesday, January 23, 2001 8:30 PM
> To: filmscanners@halftone.co.uk
> Subject: filmscanners: metamerism and Epson 2000P
>
>
> Here's a page specifically devoted to metamerism and the 2000P:
>
I don't think this article is using the term correctly to describe the
phenomenon they are referring to. To quote Wyszecki & Stiles in "Color
Science", "Metameric color stimuli are color stimuli with the same
tristimulus values but different spectral radiant power distributions.
An
equivalent definition states that metameric color stimuli are color
stimuli
that have different spectral radiant power distributions but match in
color
for a given observer." (p. 184) Thus, metameric refers to two different
objects having the same tristimulus values under the same illumination
but
different spectral reflectances. This article talks about the same
object
having different tristimulus values under different illuminations, just
the
opposite of the definition! The odd thing is, the article starts with
the
correct definition, then goes on to use it in just the opposite manner
in
which it is defined.
Frank Paris
marshalt@spiritone.com
