Re: Metamerism vs Color Constancy
Re: Metamerism vs Color Constancy
- Subject: Re: Metamerism vs Color Constancy
- From: <email@hidden>
- Date: Tue, 20 Sep 2005 00:47:30 -0400
Marco,
As you mentioned, "metameric" can be used with both
"match" and "failure". It is always relative to another
media which ideally has the same color under at least one
illuminant.
Color constancy, usually characterized by its antonym,
"Color Inconstancy" Index (CII), is always relative to one
color patch as seen with various illuminants.
While it could be said that some brands of printer inks
show metameric failure for certain illuminants, it could
also be said that some colors will show color inconstancy.
The problem is that just saying that an ink is metameric
does not scientifically mean that the match is good or
bad. In fact, saying that an ink is metameric is just true
since all color reproduction is done with metamers (CRTs,
LCDs, prints, film). However, many only see a negative
side to the word, thus its misuse.
Danny Pascale
dpascale AT babelcolor DOT com
www.BabelColor.com
On Mon, 19 Sep 2005 20:51:43 -0700
Marco Ugolini <email@hidden> wrote:
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>):
------
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").
If 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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