Metamerism
Metamerism
- Subject: Metamerism
- From: "Bob Binder" <email@hidden>
- Date: Fri, 26 Oct 2001 10:14:59 -0400
- Thread-topic: Metamerism
In a message dated Thu, 25 Oct 2001 07:51:28 EDT, C. David Tobie writes
- "Despite the objections of the technically minded, we are witnessing
the development of a new meaning, or perhaps a couple of new meanings,
for an existing term."
C. David may be correct, but I fear if we allow this to happen, we risk
diluting the original and correct meaning of the term. Maybe this is
advancement, but in my opinion, it is not. Apparently I am one of the
"Technically Minded" folks he refers to.
Metamerism is the phenomenon that occurs when the color of two items
match under one light source but do not match under another. Color is
the result of the interaction between an object being viewed, the light
source illuminating the object, and the receptor viewing this object.
Metamerism occurs when the spectral response curves of two or more items
do not match, but the combination of the above three elements intersect
such that the XYZ values are the same. This causes the color to be the
same, given this specific and unique combination of objects, light
source and observer. Change the light source and they may no longer
match. (Alternately, change the observer, and they may no longer match).
If the spectral response curves of two items are the same, they are not
metameric. In this case the color will stay the same under alternate
light sources.
Metamerism by definition always involves two or more objects. The
phenomenon where a single object changes color as the light source
changes is not metamerism. Remember, objects do not contain an inherent
property known as color. They do have very specific spectral response
curves, but this is not color. By definition the sensation of color
involves the object, the light source, and the observer. Change any one
of these three elements and the color itself has changed. So, take a
proof or any other object and move it from one light source to another.
If the color of this item appears to have changed, it has not done so
because of metamerism, it has done so because the color itself has
actually changed.
Likewise if a proof and print match each other in one light source but
deviate from one another as we move to another light source, this is
metamerism. The color or balance of a single proof changing as we move
from one light source to another is not metamerism.
Like many things, such as dot gain, metamerism is neither good nor bad,
it just is. What is important however is that we understand what it is
and how it affects us in our work. In fact, in a very real sense
metamerism is one of our best friends. If metamerism did not exist color
management would not exist, for it is what allows us to match the
physical output between different devices to each other, and to the
displays on our desktop. (As Hanz and Franz would say - something to
hear now and think about later.)
Bob Binder
Senior Applications Specialist - Digital Imaging
X-Rite, Incorporated
www.xrite.com