Digital BW, The Print

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.  :)

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "carlislematthew 
<carlislematthew@h...>" <carlislematthew@h...> wrote:

> 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? 

Peaky spectra **IS** what causes metamerism, regardless of whether 
you're talking about inks or paint chips or geology minerals! The 
physics and perceptual science of metamerism is not in question.

The cones in your retina have three very broad and overlapping 
sensitivity curves, but all three centered in the middle (430, 530, 
560 nm)  However real-world pigments and light sources often have 
sharp peaks and valleys and their peaks are often higher or lower 
than the cones' peak sensitivity.  If the reflectance spectrum of a 
pigment and the emission spectrum of light source both have, say 
sharp peaks at 680 nm and 540 nm the resulting color will look 
yellow.  Shift the peak of the emission spectrum to, say, 500 nm and 
the light will look only a LITTLE different to the eye, but the 
pigment will look red.

> Does this really mean that the yellow ink goes magenta in
> tungsten light and green in daylight?  

No one is proposing that the yellow ink changes color, and if you're 
a "scientist by nature" you wouldn't ask such a question.    The 
color you see is a result of the COMBINATION of wavelengths hitting 
your retina.   So If you have equal amounts of red, green, and blue 
hitting your retina you see white (or grey).    Remove (or reduce) 
the yellow because its reflectance peak(s) don't line up with the 
emission spectrum and the result is that cones with the middle 
spectral sensitivity (530) nm don't receive as much stimulation so 
your eye sees a different color.

The inkjet makers make their job more difficult by using 7 inks.   
The eye only has 3 photopigments for color perception.  Getting all 7 
to play nice together is like herding cats.   

None of this proves the yellow ink theory - as I've said before here, 
anyone with a decent hi-res scanner that can show the individual dots 
should be able to post sample images of IP and Epson grayscale images 
so we can SEE what inks it's using and count the relative number of 
dots of different colors.   I posted such images wrt a Black-Only 
discussion but I don't have IP.

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "plnelson2003 
<peter@s...>" <peter@s...> wrote:
> Peaky spectra **IS** what causes metamerism, regardless of whether 
> you're talking about inks or paint chips or geology minerals! The 
> physics and perceptual science of metamerism is not in question.


Just a followup to this for anyone with an interest in science.

Most science museums have little metamerism demo's.  The
one in Boston, for instance, has one with 2 little boxes
each lit seperately, and pile of colored chips.   The boxes
LOOK like they're lit with the same color light and if
you put your hand in it (usually) looks about the same in
both boxes.  But if you pick up a chip and put it in one
box the chip looks yellow; put it in the other and it looks
black.

You can easily make your own metamerism box to amuse yourself,
your friends and your kids.  Make two boxes and light the
inside of one with a small fluorescent tube used for a
softbox.  Go down to Radio Shack and buy red, green, and 
blue LED's (It's a good idea to buy several of each for 
more light and better diffusion.)  Light the inside of
the other box with the LEDs.  LED's have a very narrow (typically
20 degree) angle of "out"cidence so you will have to fiddle
with pointing and diffusing them to light a spot in the box
evenly.  Adjust the levels of the LEDs with resistors or extra
diffusion so they are balanced to white.

LED's have EXTREMELY narrow output spectra - just a few
nm wide!  So even though the light will look white to
your eye, the peaks will often fall totally between 
the reflectance spectra of many common dyes and pigments.

Find common household items, of different colors and place
them in the fluorescent box where they should look normal,
and then in the LED box where they will sometimes have a
dramatically different color.  It will be common to find items
which look purple in one box and blue in the other or yellow
in one and green in another, or that are a bright color in one 
and turn nearly black in the other, etc.   It's a great 
introduction to the physics and perceptual science of color
for kids and adults.

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "plnelson2003 
I wrote . . . 

> You can easily make your own metamerism box to amuse yourself,
> your friends and your kids.  Make two boxes and light the
> inside of one with a small fluorescent tube used for a
> softbox.  

I meant "lightbox".   A tube for a softbox would be rather, er, 
*bright*.

Good information - thanks.

> 
> Peaky spectra **IS** what causes metamerism, regardless of whether 
> you're talking about inks or paint chips or geology minerals! The 
> physics and perceptual science of metamerism is not in question.
> 
> The cones in your retina have three very broad and overlapping 
> sensitivity curves, but all three centered in the middle (430, 530, 
> 560 nm)  However real-world pigments and light sources often have 
> sharp peaks and valleys and their peaks are often higher or lower 
> than the cones' peak sensitivity.  If the reflectance spectrum of a 
> pigment and the emission spectrum of light source both have, say 
> sharp peaks at 680 nm and 540 nm the resulting color will look 
> yellow.  Shift the peak of the emission spectrum to, say, 500 nm 
and 
> the light will look only a LITTLE different to the eye, but the 
> pigment will look red.
> 
> > Does this really mean that the yellow ink goes magenta in
> > tungsten light and green in daylight?  
> 
> No one is proposing that the yellow ink changes color, and if 
you're 
> a "scientist by nature" you wouldn't ask such a question.    The 
> color you see is a result of the COMBINATION of wavelengths hitting 
> your retina.   So If you have equal amounts of red, green, and blue 
> hitting your retina you see white (or grey).    Remove (or reduce) 
> the yellow because its reflectance peak(s) don't line up with the 
> emission spectrum and the result is that cones with the middle 
> spectral sensitivity (530) nm don't receive as much stimulation so 
> your eye sees a different color.

A scientist by nature is someone that questions, wants to know how 
things work, applies logical thinking to problems and so on.  i.e. 
not someone who knows everything about color, pigments and the eye.

In my short time on this forum I've noticed you rub a lot of people 
up the wrong way during your many posts.  I think you need to relax a 
little bit and get less enjoyment out of harshly correcting people 
and knowing more than others on a particular subject.