Re: metamerism and metameric color - more
Re: metamerism and metameric color - more
- Subject: Re: metamerism and metameric color - more
- From: Rudy Vonk <email@hidden>
- Date: Wed, 20 Jun 2001 17:07:45 +0200
I apologize profusely if I have missed something at the beginning of
this thread (for being on holiday) that invalidates my post, but I find
what little I have read in it very interesting. For its own
repetitiveness, I humbly take issue with Samer Mady for his statement:
>
again we
>
have to stick to the definition of metamerism ( two colors possesing the
>
same trichromatic values but differ in the spectral distribution)
This cannot be a valid definition (with respect). Obviously, the two
objects *must* have different spectral distributions or they would
*always* look the same, so this part of the definition is merely stating
the obvious. The other part of the suggested definition fails to state
the essential: metamerism means that two objects produce the same
tristimulus values (to us, the signals interpreted by our brain from
three types of cones - to our computer, XYZ values or similar calculated
from reflectance power distribution measured in a spectrophotometer)
UNDER ONE ILLUMINANT and different tristimulus values under another. I
think it is worth while clarifying this...
As for the white apple, I am not in the least questioning Harvey's,
Samer's or Igor's arguments - I simply am in no position to without
either trying it or boning up on the literature - but I agree with
Igor's rebuttal of Ernst's example (clearly if the illuminant were a
single wavelength, a "white" body would reflect it, and so would a
"colored" object that doesn't absorb that wavelength, and they'd both
look the same).
As for this fantastic "white point adaptation" postulated (or documented
- he obviously knows a lot more about it than I do) by Igor I have two
questions. First, why doesn't the entire red room look just as white as
the apple is supposed to. I have been in rooms, albeit not red rooms,
illuminated by red light (not in Amsterdam, BTW) often enough to know
that they don't look white to me. They look red (as in a dark room, for
instance). Second, when I wake up in the middle of the night in a
strange hotel room with an urgent physiological need, and can't find the
light switch,... OK, no, this is not a valid example, because if there
is no physical light to be reflected, there is nothing there for my
brain to interpret :-)
--
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Rudy Vonk
Oviedo, Spain
<email@hidden>
+34 607 354100
You can't always want what you get.
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