Metamerism vs color inconstancy [was: GRACoL: Very surprised...]
Metamerism vs color inconstancy [was: GRACoL: Very surprised...]
- Subject: Metamerism vs color inconstancy [was: GRACoL: Very surprised...]
- From: Marco Ugolini <email@hidden>
- Date: Thu, 29 Apr 2010 11:14:23 -0700
- Thread-topic: Metamerism vs color inconstancy [was: GRACoL: Very surprised...]
In a message dated 4/29/10 10:30 AM, Ken Fleisher wrote:
> Ben,
>
> I can understand your frustration, but that's just the physics of the
> situation. We often think of metamerism as a bad thing (none of us like to
> encounter metameric failure, as you have described in your posts), but
> metamerism is the mechanism that allows us to use just four printing inks
> (sometimes three, sometime more) to represent a large gamut of colors.
> Without metamerism, we could not do this.
>
> The trade-off is that we are making metameric prints, which means they are
> dependent on the illuminant. The solution to this dilemma is a new technique
> often called "spectral printing", which is currently a hot research topic in
> the color science and printing circles. With a limited set of printing inks
> (even six, or eight), you will never have a print that looks correct in all
> viewing conditions, but with spectral printing, we will be able to optimize
> our prints for more than one illuminant. I've seen prints that look correct
> under both tungsten and D50!
>
> It will be a while before we see this in common use, but it "is" on the
> horizonĀ
Ken,
I both agree and disagree.
I agree that metamerism is the phenomenon thanks to which (as far as prints
are concerned) we are able to match colors between TWO prints made with
inks/pigments/papers of different SPDs (spectral power distributions) when
viewed under ONE illuminant. That would be what is properly called a
metameric MATCH, which in our example would always involve TWO prints and
ONE illuminant.
But (and I have made this point before) when the appearance of ONE print
changes upon changing illuminant (for example, causing a visible color cast
in its neutrals), that should NOT be called "metamerism".
That is called COLOR INCONSTANCY instead, described as the failure of a
"normal" human observer in removing the effects of a change in illuminant
upon the perception of color in objects. (Note: the process which DOES
remove the effects of the illuminant upon color appearance is also referred
to as "discounting the illuminant".)
To encourage a discussion of the distinction which I am attempting to
illustrate, I would refer you to that now-ubiquitous medium of
knowledge-sharing, Wikipedia, (as imperfect as it may be and with all its
limitations, it's still quite useful) -- and submit to your attention its
definitions of:
METAMERISM: <http://en.wikipedia.org/wiki/Metamerism_(color)>
COLOR CONSTANCY: <http://en.wikipedia.org/wiki/Color_constancy>
Of course, there is far more to the subject than what one finds in
Wikipedia, but it's a start.
Best.
Marco
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