Re: Metamerism
Re: Metamerism
- Subject: Re: Metamerism
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Wed, 31 Oct 2001 15:33:14 -0600
In the unlikely case that this dead horse has not yet been sufficiently
flogged, I have assembled what I think is an exhaustive list of metameric
cases. Of the twelve cases, seven involve two observers, and therefore are
theoretically possible, but of little practical interest. The remaining
five (1a, 2a, 2b, 2c and 3a) are the ones that matter.
In the following list, "different" means spectrally different and
"identical" means spectrally identical.
1. Emissive Cases (e.g. a monitor image)
1a) A single observer views two different lights. If they match, it is
metameric.
1b) A single light is viewed by two individuals, each having a different
visual response (e.g. one individual has color defective vision). If they
match, it is metameric. ("Match" in the cases involving two observers is
defined in the notes that follow.)
1c) One observer views one light and a different observer views a different
light. If they match, it is metameric.
2. Reflective Cases (e.g. viewing a print)
2a) A single observer views two identical prints, each illuminated by a
different source. If they match, it is metameric.
2b) A single observer views two different prints, each illuminated by the
identical source. If they match, it is metameric.
2c) A single observer views two different prints, each illuminated by
different sources. If they match, it is metameric.
2d) Two different observers view a single print illuminated by a single
source. If they match, it is metameric.
2e) One observer views a print under one source, while a different observer
views an identical print under a different source. If they match, it is
metameric.
2f) One observer views a print under one source, while a different observer
views a different print under the identical source. If they match, it is
metameric.
2g) One observer views one print under one source, while a different
observer views a different print under a different source. If they match,
it is metameric.
3. Mixed Cases (e.g. comparing a monitor to a print)
3a) A single observer views a colored light and also a print under some
source, such that the spectrum produced by the source reflecting off the
print is different from the spectrum from the colored light. If they match,
it is metameric.
3b) One observer views a colored light while a different observer views a
print under some source, such that the spectrum produced by the source
reflecting off the print is different from the spectrum from the colored
light. If they match, it is metameric.
Notes:
In cases 1b, 1c, 2d, 2e, 2f, 2g and 3b the "match" occurs in two different
brains, so it must determined strictly from the XYZ values (assuming the
response functions of the two different observers are known).
All of this derives directly from the CIEXYZ standard. It completely ignores
important things like viewing conditions, adaptation, etc.
--
Bruce J. Lindbloom
www.brucelindbloom.com