Re: Metamerism vs Color Constancy
Re: Metamerism vs Color Constancy
- Subject: Re: Metamerism vs Color Constancy
- From: <email@hidden>
- Date: Tue, 20 Sep 2005 09:25:25 -0400
Hello Marco,
You mention:
...when talking of any one set of printer inks,
we are NOT matching pairs of samples exhibiting
different spectral characteristics.
When we compare the printed results of a given ink set to
prints/displays/photos whose color comes from other
materials (dyes/pigments/RGB primaries), we do compare
them to samples with different spectral charateristics. A
metameric comparison is not done between samples obtained
from the same dyes/pigments/RGB primaries, whereas color
inconstancy is done against iself, and thus with the same
spectral constituents.
We could say that some Epson inks show metameric failure
against a set of offset printing inks, or against other
sets of Epson inks. Because this comparison is seen by
changing the illuminant, it is easily confused with color
inconstancy which is also happening; these are just two
effects of the same phenomena. Please note that the color
inconstancy index does not have to, and will generally not
be equal to the metameric color difference (even if
computed with the same color difference equation).
Just imagine that you have the same color from two sources
(ink and paint for example); if they both show the same
color inconstancy under two given illuminants, they could
well be metameric matches... (for some illuminants, maybe,
but not garanteed!).
A more likely case for both metameric match and color
inconstancy would be for two shades of a color (I have
measured this for kaki green paints of the same
manufacturer for instance). You can look at this screen
shot that illustrates this example:
http://www.babelcolor.com/main_level/screen_shots/Spectral_Tools_MI.htm
Since the two shades are made of the same pigments, there
is basically no metameric effect between the two (i.e. the
color relation or color difference remains the same for
various illuminants). However, these colors can be color
inconstant and become "browner" when seen under D50
relative to tungsten (Ambient 2775 K). Since they both
become "browner" at the same time, the relative hue,
saturation and brightness difference is about the same.
I hope this makes it clearer!
Danny Pascale
dpascale AT babelcolor DOT com
www.BabelColor.com
On Tue, 20 Sep 2005 00:19:17 -0700
Marco Ugolini <email@hidden> wrote:
In a message dated Tue, 20 Sep 2005 00:47:30, Danny
Pascale wrote:
While it could be said that some brands of printer inks
show metameric failure for certain illuminants, it could
also be said that some colors will show color
inconstancy.
Hello, Danny.
I fail to understand how it is that it can be said that
certain printer inks
show metameric failure for certain illuminants: after
all, when talking of
any one set of printer inks, we are NOT matching pairs
of samples exhibiting
different spectral characteristics.
Could please explain more specifically?
Thank you.
--------------
Marco Ugolini
Mill Valley, CA
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