Digital BW, The Print

There was a discussion on the List recently about "metamerism".  At 
the time, I was unfamiliar with this word but thought I had gotten 
the gist of it's meaning from the context of the posts, such as this 
one from Jeff M.:

>All things in life will look slightly different under different 
lighting conditions... and these inksets reflect that. If you try and 
print a grayscale image using Epson color OEM inks... then you will 
see METAMERISM. The print totally changes color under different light 
sources. The Epson OEM inks are so bad with metamerism that I find it 
an obstacle even for color images.<

Well, I finally got around to pulling out the dictionary a few 
moments ago and now I'm thoroughly perplexed.  I'm guessing that I 
need a better dictionary because my copy of the American Heritage 
Dictionary defines metamerism as: "The condition of having the body 
divided into metameres".  Ok.....well then, it goes on to define 
metamere as: "One of a series of homologous body segments, as in 
worms and lobsters".

Anyone got a better definition of metamerism at hand?  Maybe from a 
complete set of the Oxford English Unabridged Dictionary 20+ 
volumes?  American Heritage just doesn't cut the mustard.  ;-)

Gary Benson
Eagle River, Alaska

Hi Gary,

Your dictionary is correct, just a little off in it's context. This from a
color science glossary.

Metamerism
A metamer which match each other under one set of conditions but mismatch
when viewed under another.

Metameric Colour Samples (Metamer)
A pair of colours which differ spectrally but which yield the same or
similar tristimulus values under at least one set of viewing conditions.

You may find this interesting:
http://www.tssphoto.com/sp/dg/2000p/metamerism.html

Then again... I kinda like the lobster definition better ;-)  Sometimes my
color prints shift color so drastically you'd swear I'd cooked them!


Carolyn

> Well, I finally got around to pulling out the dictionary a few
> moments ago and now I'm thoroughly perplexed.  I'm guessing that I
> need a better dictionary because my copy of the American Heritage
> Dictionary defines metamerism as: "The condition of having the body
> divided into metameres".  Ok.....well then, it goes on to define
> metamere as: "One of a series of homologous body segments, as in
> worms and lobsters".
> Anyone got a better definition of metamerism at hand?  Maybe from a
> complete set of the Oxford English Unabridged Dictionary 20+
> volumes?  American Heritage just doesn't cut the mustard.  ;-)

Gary,

I frankly prefer to think of worms and lobsters as metameric than what I am 
about to say, but here goes:

Our eyes see color in ink because not all wavelengths of light are reflected 
back from the dye or pigment particle in the ink. So far so good, right? 

However you can have the sensation of a given color as a result of a 
discontinuous spectral reflection; meaning a combination of spectral "peaks" 
that arrive at your eye and get mixed together to give you a color. Alternatively 
you can have that same color (or very close to it) by a continuous "chunk" of 
spectrum.  Whether a given ink color reflects continuous or discontinuous 
spectra wouldn't matter if we always got the same sensation and saw the 
same color. But...

In order for us to see, we need light, right? Light can also be made up of a mix 
of spectral frequencies, hence, for example  we have different "color 
temperatures", as well as different color of light itself. Once again, not all light 
is made up of a smooth, continuous mix of frequencies - as the sun may be, 
for example. Fluorescent lights (especially the cheap kind) are notorious for 
discontinous spectra. 

So, when we put  inks of discontinous spectral reflections under all the 
various possible light sources (sun, incandescent, fluorescent, etc) they tend 
to react differently than inks with a continuous spectral makeup. The latter 
hold up their color better.  The ones with discontinuous spectra have a hard 
time maintaining their color:  they can't reflect back  their particular  mix of 
frequencies in the same exact proportions under all the different light sources. 
Hence their color appears to our eyes to shift. 

I am afraid this is a very abbreviated description of a subject for which you 
better look up a scientific source and not the American Heritage Dictionary! 

In practical terms, it means that some color inks exhibit metamerism because 
they don't hold up their color well in daylight and artificial sources. They may 
have been optimized for color gamut, permanence, freedom from clogs... all 
sorts of other variables, but not that particular one. It's just one more thing to 
look for when judging the performance of color inks - especially if you are 
trying to maintain neutrality across a gray scale.

I hope this helps - even a tiny bit.

Antonis





--- In DigitalBlackandWhiteThePrint@y..., "Gary Benson" <bensonga@g...> 
wrote:

...
 Ok.....well then, it goes on to define 

> metamere as: "One of a series of homologous body segments, as in 
> worms and lobsters".
> 
> Anyone got a better definition of metamerism at hand?  Maybe from a 
> complete set of the Oxford English Unabridged Dictionary 20+ 
> volumes?  American Heritage just doesn't cut the mustard.  ;-)
> 
> Gary Benson
> Eagle River, Alaska