Re: Neutral grey under different lighting
Re: Neutral grey under different lighting
- Subject: Re: Neutral grey under different lighting
- From: Graeme Gill <email@hidden>
- Date: Tue, 04 Sep 2007 23:21:05 +1000
Fleisher, Ken wrote:
A metameric mismatch can only occur between two metameric colors.
I can't agree with that. Metamers are two different spectral distributions
that appear identical. It is simple logic therefore that two spectral
distributions that do not appear identical, are not metamers.
That is,
they must match under one illuminant but not another.
I don't think this has anything directly to do with the definition of metamerism.
The fact that you are creating spectral distributions using
a light source and a tinted surface is just a practical spectral source.
Yes, this mechanism gives different spectra if you change the illumination.
It's the spectrums that are the metameric stimuli, not the reflective sample
colors though.
> Non-metameric colors
are either 1) the same identical color (i.e. SPD) so that they match in
every condition or 2) they never match. (Okay, parametric colors "almost"
match, but technically that's still not metamerism.) Therefore, they cannot
produce a metameric mismatch as you suggest.
Again, I can't agree. Two reflective sample colors may be potential
sources of metameric colors if illuminated with the correct illumination.
Under other illumination they are not metamers, since their colors appear
to be different (this is from the basic definition of metamerism).
Metameric failure is simply when a metameric pair does not produce a match
under a particular viewing condition--I've never heard of it described in
relation to whether it is "intended" to produce a match or not, it simply
doesn't.
Talking about "metameric failure" doesn't have any meaning otherwise. It's
of little significance that two colors look different (they aren't metamers),
it's only of interest if they are intended to be metamers, and are not so
due to some failure in the source of the colors.
Your summary also implies that you should only call two colors metameric
under the condition where they match, but a metameric pair is still a
metameric pair no matter what conditions they are observed under and whether
they match or not.
Metamers ("metameric stimuli") by definition are two different spectrums that
appear to be the same color. If they don't look the same color, they are not
metamers. (You can check this definition in standard references such as
Wyszecki & Stiles or Judd & Wyszecki etc.) The eye's three color sensor each
weight and sum the spectrum they receive differently, and it's a mathematical
property of this process that there are (in general) and infinite number of
different spectrums that will produce each possible combination of responses
in the three sensors. This property is what gives rise to metameric matches.
Graeme Gill.
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