Re: metamerism
Re: metamerism
- Subject: Re: metamerism
- From: neilB <email@hidden>
- Date: Tue, 19 Jun 2001 00:08:41 +0100
Paul
On 14-6-01 at 11:29 PM, email@hidden (Paul Guba) wrote:
>
So how are we defining metamerism here? How is it exhibited in the
>
epson prints? Is it only in certain colors? Does it appear more on
>
some papers than others? I would like to know so I can blame my bad
>
prints on it.
you might find the follwing helpful
"kenward.rfe" wrote:
>
> Metamerism is where the relationship between
>
> colours alters, sometimes drastically when the print is viewed under
>
> different illumination types. It is not the overall colour change that
>
> comes from moving from one light source to another.
Al Edgar replied:
This is an expanded technical note on metamerism.
Cyan dye absorbes red light, not green, and not infrared. Where
does red become infrared? The human eye falls off gradually as
red deepens into infrared. If the cyan dye opens too soon in the
near infrared, then the eye sees that infrared as red. This
makes the cyan dye appear weak under light that is rich in
infrared, such as an incandescent light, and a print made with
that cyan will have reddish grays under infrared rich light. If
you boost the amount of cyan to neutralize gray under
incandescent light, then under light that has no infrared, such
as flourescent, the cyan will be too strong and grays appear
cyanish green.
Too bad they don't offer a cyan dye that overabsorbes infrared,
because it would have a reverse metamerism, making grays cooler
under warm incandescent light, and warmer under cool lights like
flourescent and daylight. Physics does not preclude such cyans,
they exist, but dyes that absorb infrared are more rare, and will
not end up in an ink cartridge unless someone looks for them
specifically.
One way around metamerism is to use 100% undercut on the K, so
cyan does not enter into the reproduction of gray. Maybe this is
what Epson does on the 10000. Just a guess. This "fix" however
has problems as brighter colors that must use cyan will still
shift, and the dots of ink jet dither are stronger with 100% K.
Because Epson does not give us artists access to CMYK directly,
we have no control over any of this anyway. Does Roland?
Metamerisms can happen with other colors too, but the effect at
the edges of infrared produces the strongest problems. It is
responsible for the greenishness of flourescent lights (and
extreme orangishness of incandescent) on film, the "pink violet"
effect when photographing flowers, and black pants turning orange
with some video cameras.
Silver absorbes all colors, including infrared, almost equally,
so Ansel Adams never had this problem.