Re: Epson Stylus Pro 9600 Extrachrome
Re: Epson Stylus Pro 9600 Extrachrome
- Subject: Re: Epson Stylus Pro 9600 Extrachrome
- From: Graeme Gill <email@hidden>
- Date: Tue, 16 Nov 2004 10:50:30 -0800
Roger Breton wrote:
I'm under the impression that the change in appearance of color triggered by
a change of illumination is aply called illuminant metamerism.
I don't think that is accurate. Metamerism is when two stimuli have
different spectrum, but appear the same color. If you illuminate a
reflective surface with two different light sources, it would be
unusual if the resulting reflected spectrum didn't change in appearance.
It's nothing to do with metamerism, it's just the product of the light
spectrum and the surface reflectance spectrum.
In this
equation, the observer is constant, me. So, what is it that causes the
change in appearance if not the change in lighting conditions?
But the change in appearance is expected. You can't avoid it.
What is usually a problem is that your original and proof change
in different ways under different illuminants.
The whole mechanism of obtaining a tristimulus match (ie. designing two
different shaped reflectance spectra to be a metameric pair under a given illuminant)
is such that you absolutely expect them to not be a match under a different illuminant.
If the two reflectance spectra continue to have the same appearance under a variety
of illuminants, then they must be a spectral match.
Are you saying compare the spectral reflectance of the CMYK inks of inkjet
inks to those of the offset inks I'm trying to simulate?
Yes.
> If the spectral
reflectances are remotely similar between the two systems there are good
chances I will see a match over a broad range of illumination?
That should be the case (modulo how differently the colorants mix).
At what point would you say the match is going to stop working? Any idea on how to
quantify that?
The standard way of quantifying this would be to either measure and/or calculate
the delta E under an illuminant other than the one they are designed to be
a tristimulus match under.
Graeme Gill.
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