Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Alan Zinn 

> According to your helpful web page I learned that metamerism
> has to do with adjacency of individual specs of color in 
> both the spatial and hue dimensions.    If the printer
> driver favors a certain color dot or pattern metamerism
> is more severe.  Reminds me of tiny Albers squares and the 
> simultaneous contrast phenomenon.  Did I get that right?

No.

The adjacency has nothing to do with it.  If you read
carefully you'll see that the discussion of dot patterns
was in the section describing dithering, not metamerism.

Metamerism results from the fact that light sources do not
produce smooth output at all wavelengths and pigments do not
reflect light equally at all wavelengths.  Both exhibit 
spectral peaks and valleys.   If the peak reflectance 
wavelength of a pigment happens to fall in between two
emission peaks of a light source the result will be reduced
intensity for whatever color that pigment is supposed to 
represent. 

Many science museums (e.g., the one we have here in Boston)
have metamerism displays.   At the Boston one they have
two light boxes with light that looks (to the eye) to be the
same.   They also have a basket of colored chips.  Some of the 
chips look the same in both boxes.   But some of the chips
change dramatically, for instance they have one that looks
yellow in one box which looks almost black in the other.

You can do this yourself with LEDs.  LEDs have VERY narrow
spectral output -  only a few nanometers.  You can make two
lightboxes with "white" light by combining Red, Green and
Blue LEDs - but use ones from different manufacturers so
they have slightly different spec's.  Then find various
colored objects and compare them in both boxes.  Most things
will look the same but some will shift dramatically.  I've
done this and it's fun (if you're a science nerd like me).