Digital BW, The Print

I agree that we haven't proven scientifically that the yellow ink is the
source of the metamerism.  I can tell you though what testing I have done
that help support this.

1.  I'm not aware of a device that can accurately measure metamerism -- at
least one that is affordable to the general public.  All  spectros that I
know of use their own light source to illuminate the target, and the
characteristics of this light source cannot be changed.

2.  I've looked at prints of a 21-step grayscale wedge from the Epson Driver
and IP under both a loupe and a microscope.  Most of my focus has been on
the lightest patches (1-5%) since it is easiest to see the individual ink
droplets there.  Here is what I've observed:
a. The Epson Driver uses yellow ink.
b. The Epson Driver's "black only" setting does not use the LightBlack ink.
It only prints with the Black ink.
c. ImagePrint uses MatteBlack, LightBlack, LightMagenta, and LightCyan when
printing in "grayscale" mode.
d. ImagePrint changes the proportion of LightMagenta and LightCyan as you
adjust the TintPicker.

3. I've cut open "empty" cartridges of MatteBlack and LightBlack ink and
smeared the remaining ink on paper.  The light black ink is very warm in
tone.  It is more difficult to see with the MatteBlack ink, but it also
appears somewhat warm in tone.  Furthermore, Prints using the Epson Driver
with the "black only" setting are warm and prints using the combined
MatteBlack and LightBlack inks are warm. (I used the ink reduction settings
of IP to print using only MatteBlack and LightBlack).

4.  My office is lit by flourescent light and has blinds covering an outside
window.  The blinds can be adjusted so the daylight is not overpowering the
flourescent.  I can then turn a print back and forth between the window
light and flourescent light and *easily* see the shift from green to magenta
in the Epson Driver prints and the Epson RIP prints.  I don't see this in
ImagePrint prints.

So, my conclusion is:
a. ImagePrint uses the LightCyan and LightMagenta to neutralize the inherent
warm tone of the MatteBlack and LightBlack inks.
b. ImagePrint adjusts the proportions of LightCyan and LightMagenta ink to
tone the prints via the TintPicker.
c. One of the other inks: Yellow, Magenta, or Cyan (or a combination of
them) suffers from metamerism.
d. I don't care which one or combination causes metamerism as long as I have
a solution and can prevent it.

Conclusion (d) is not entirely true.  I am curious and would like to know,
but I'm not losing sleep over it.  I have a printing solution that works
well, so I can go out and take more pictures.

For the curious, I would suggest further testing by someone (not me) of the
Epson RIP.  Dial down the yellow ink so it is not used at all and then
create a profile through the RIP.  Use that profile to print a grayscale
image and then evaluate it for metamerism.  This process could be repeated
for Magenta and Cyan as well.  I'm not sure it would be possible to get
neutral prints with this method since I suspect the ink reduction occurs
*after* the rendering engine has done its thing.  Perhaps a high-
end profiling tool could do this?

--Tom

----- Original Message -----
From: <carlislematthew@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Wednesday, February 19, 2003 11:58 PM
Subject: [Digital BW] UC metamerism, yellow ink & confusion


> I keep hearing that the metamerism is caused by the yellow ink, and
> that the IP RIP (and others) reduce/remove the metamerism by not
> using that particular ink.  I also heard once that is was the magenta
> ink that was the issue, but that view seems very much in the minority
> these days.
>
> In support of the "yellow=bad" crew, I've seen posts that say that IP
> prints have been looked at very closely under a loupe and that no
> yellow ink is used.  The same people say that metamerism is gone.
> Where I begin to lose faith is when people link the two.  Soooo,
> we're not using yellow ink, and we have no metamerism, therefore the
> yellow ink must have caused the metamerism!!!  YAY!!!  Problem
> solved!!!!!
>
> Using similar logic, I drank some Hales Cream Ale tonight (very nice
> beer BTW) and I did not suffer from a major heart attack.  So
> therefore I logically conclude that the beer saved me from dying.
> Riiiight.
>
> When people have asked WHY not using the yellow ink prevents
> metamerism we start to throw scientic terms around and nobody wants
> to admit that they don't know what's going on.  Apparently, the
> yellow ink has a "peaky spectral response".  Lovely.  Everyone nods
> their heads and mutters "yes, peaky spectral response - that makes
> sense".  Does it though?  Does this really mean that the yellow ink
> goes magenta in tungsten light and green in daylight?  Anyone printed
> a yellow test strip and done some kind of scientic measurement on
> it?  Or perhaps the yellow ink reacts to other inks when used
> together and makes the other inks change colors in different
> conditions.  Who knows...  Peaky spectral response?  Sure.
>
> I'm a scientist by nature.  I like to know WHY things happen.
> Unfortunately, I'm not satisfied with "peaky spectral response".
> Could someone please tell me (and everyone in this group) how this
> relates to metamerism in this case.  Be very specific, because there
> are a lot of smart people in this group.
>
> Finally, I'd like to propose the crazy, insane theory that the lack
> of yellow ink has nothing to do with the reduction in metamerism.
> Perhaps producing a neutral(ish) print with the blank and light-black
> (dark yellow!) inks really doesn't need yellow ink.  Maybe there's
> more yellow than we can eat, and putting more down would just make
> everything look, well, yellow?
>
> It may sound like I'm annoyed about all this.  In fact, I'm not.
> I've been contributing to this group a little over the past few
> weeks, but have mostly been lurking and learning.  I have MIS VM inks
> on order and Paul's curves waiting in anticipation for use on my old
> 1280, so I think I'll be just fine.  :)
>