Re: Print Quality

Jonathan Bailey wrote:

> OK. I'll ask.... what is metamorism?? Thanks - JB
>

Metamerism is a non linear, disjunctive, shift in perceived (or
reflected/measured) color when the ambient lighting temperature changes.
It's often called a "color shift" but that is an inaccurate description.

Now to REALLY explain it... The human eye and mind combination can
easily accommodate a wide range of lighting "colors" and adjust
accordingly.. For example, the color (spectrum) of light emitted by
tungsten lights and by the sun differs significantly. However, if I
take a red apple from one lighting condition to another, my mind easily
adjusts for the variance in color of the ambient light and I still see
the apple as the same red. That's possible because the red apple's
reflected colors are relatively uniform across the tonal range of
visible light.

In instances of metamerism something different happens. At particular
points in the spectral (hue) range, instead of the response being smooth
and predictable, instead of it remaining in sync with the change in
ambient light and the response of other colors on the print or object
viewed, it departs from that linear response.

Let's say you are looking at a neutral B&W print under tungsten light
and one ink used is significantly metameric. You then move the print to
daylight conditions and it looks greenish. This happens because that
ink, instead of giving a response in sync with the other inks, diverged
towards the green hues instead. The problem is that if I then
compensate in printing and print the image to be neutral in daylight, if
I move it to tungsten it looks magenta...

You can see the problems metamerism brings.. None of the effects are
positive. So, you want inksets that exhibit as little metamerism as
possible (pigments tend to be bigger offenders), or you can often use a
RIP to compensate for the metamerism of one or two inks in a set by
instructing the rip to avoid using those ink colors when printing
specific tones where the metamerism is likely to be apparent (neutrals
and skintones are most susceptible in good part because of the human
physiological sensitivity to both skintones and slight variances from
neutral).

I hope that makes it clearer.

 
Keith Krebs

"Just some guy," caretaker of the Multiverse's largest EPSON printer
User Community (highly recommended by Vogon Poets and MegaDodo
Publications), at:
http://groups.yahoo.com/group/EPSON_Printers/
and the Multiverse's largest Canon printer User Community at:
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"For the rest of you out there, the secret is to bang the rocks together
guys"

 
Received on Mon Apr 19 06:35:36 2004