Re: Color constancy and metamerism
Re: Color constancy and metamerism
- Subject: Re: Color constancy and metamerism
- From: "Dennis W. Manasco" <email@hidden>
- Date: Wed, 21 Sep 2005 05:10:31 -0500
At 12:25 PM -0400 9/20/05, Mark Rice wrote:
...
I have achieved near perfect neutral appearing prints under 5000K
lighting, but under cool white deluxe, the prints appear slightly
sepia. That is metamerism.
...
Actually that is metameric failure.
I apologize if that seems pedantic, and I know that typing "failure"
all the time is a pain, but people just trying to get their heads
around all of this have got to be pulling their hair out.
Metamerism is a word that describes the ability of the eye and brain
to conclude that two things are the same color, even though the two
things have different spectral characteristics.
Metamerism is the bread and butter of photography, printing,
painting, textiles and everyone else that works in color because it
allows, for example, an inkjet printer to use yellow and cyan inks to
fool you into thinking you're seeing a green leaf.
Metamerism failure on the other hand is a result of the fact that the
spectral characteristics of a thing and its representation _are_
different: The print of the green leaf may look identical to the leaf
itself when they are held next to each other under, for example, the
light of the noon-day sun, but that may not be true for all
illuminates. If you take the same picture and leaf and hold them
under a 60 watt bulb they may look very different. That's because the
light is much redder. One may reflect much more red light than the
other making if more yellow or orange.
A big part of the design of inks for printing (or pigments for
painting, or etc.) is an attempt to minimalize metamerism failure:
You don't want the customer's picture of yellow tulips to go green
when they take it from the gallery and hang it in their
fluorescently-lit office. You don't want your wife's perfectly
matched blue blouse and skirt to suddenly become mismatched when she
takes them from the fluorescently-lit big-box and wears them to a
party where the skirt becomes a surprising bright magenta.
Color constancy is something else entirely: It's basically your mind
fooling you about colors. It's your mind's ability to reconcile
spectral information with what it knows that information should be:
The zebra's stripes are black and white regardless of whether they're
seen by a blue-fogged morning sun or the deep red of a Serengeti
sunset -- it's still prey.
Best wishes,
-=-Dennis
(Before I get totally flamed by reputable Color Scientists: I know
that these descriptions cut a lot of corners, but I thought that they
might at least help someone figure out what is going on....)
(Now, can anyone tell me how the adjective that refers to "Any of the
homologous segments, lying in a longitudinal series, that compose the
body of certain animals, such as earthworms and lobsters." came to
refer to perceived color inconstancy under different illuminants? I
really want to know.)
.
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