Unwanted Absorptions

[joe pasky]

I read this today. It sounds counter-intuitive.

There is one highly advantageous aspect of the
so-called “unwanted absorption”: the
nonlinearity of mixing produces a gamut for
subtractive reproduction that is wider than
would be the case for ideal, non-overlapping
pigments.

Has anyone seen any data to support this argument?

Joseph J. Pasky
G7 'Expert'
Cathay America - Shenzhen China

[Erik Nikkanen]

I read this today. It sounds counter-intuitive.

There is one highly advantageous aspect of the
so-called “unwanted absorption”: the
nonlinearity of mixing produces a gamut for
subtractive reproduction that is wider than
would be the case for ideal, non-overlapping
pigments.

Has anyone seen any data to support this argument?

Joseph J. Pasky
G7 'Expert'
Cathay America - Shenzhen China

I am not totally sure I understand the question but if it is comparing over printed inks with non over printed inks there is a kind of an explanation that makes sense to me.

For a screen, if the dots are over printing, the second down dot might have less ink film thickness due to wet trap than if the two inks are printed as non overprinted dots, where the second down dot would have a normal amount of ink film.

With the two dots over printing, this will result in more white paper area between dots. This will mean that the Gamut would tend to increase in the L direction. The combination of the two inks screens whether overprinting or not runs from the maximun L value on the L axis, where the screen values are 0% out to the overprinting of the two solid inks where the screen values are 100%. Between those two points is a line that forms a ridge of the Gamut volume. This line would be different for the two conditions of overprinting dots or adjacent printing dots. The overprinted ridge line would have greater L values and have a slight hue shift when compared to the adjacent printed dots.

Does this make sense and does this describe your question?

[joe pasky]

Hmm....I don't think so.

What I assumed they were referring to is 'hue error' and 'gray value'.

I've been noodling around with the idea of wide-gamut (4-color) inks. What I've seen called 'wide-gamut ink set' has very 'clean' magenta and cyan colorants which I assume would give very low hue-error and gray-value readings.

But this published 'white paper' seems to suggest the contrary.

It just doesn't sound correct that a ink-set with a lower hue-error/gray value would reduce the gamut. I would expect the opposite.

jjp



cheers,
jjp

jjp

[gordo]

I read this today. It sounds counter-intuitive.
There is one highly advantageous aspect of the so-called “unwanted absorption”: the nonlinearity of mixing produces a gamut for subtractive reproduction that is wider than would be the case for ideal, non-overlapping pigments.

It would be nice to have a bit more of the text because this small bit seems to be confusing terms.

First regarding linearity.
All color created by halftone screening is non-linear.
We see color in presswork as a result of light being filtered by the dot of ink as well as reflected directly of the surface of the paper never having been filtered by the ink. Because we see the aggregate of the two, the effect of paper/substrate and ink need to be considered together.
Light that reflects directly off the substrate effectively contaminates the color of light that has been filtered by the ink. The result is the hue shifts color as you go from 1% dot (maximum paper color contamination) to 100% (minimum paper color contamination). This is exacerbated by the amount of optical brightners in the paper since ink is an effective blocker of fluorescence. The result is another color shift as you go from 1% dot (maximum fluorescence effect) to 100% (minimum fluorescence effect).
The non-linearity is further compounded when dots overprint because the ratio of overprinting dot areas are not consistent through the tone scale which results in a variation in trapping - at some points the dots will overprint to varying degrees while at others they will print beside each other with varying amounts of unprinted paper between them. The variation in overprinting also causes a variation in density/opacity compared to dots that print beside one another, which again affects color.
I think the only printing which would potentially be relatively linear in a color sense is collotype (continuous tone lithography).

Overprinting halftone dots does does slightly reduce gamut compared to printing dots beside one another, however both deliver a non-linear response. That being said, printing dots beside one another to try and gain the extra bit of gamut introduces other "show stopper" issues related to color shifts caused by slight misregistration - so it is not an effective strategy for increasing gamut.

If you want extra gamut, you can move to a much higher halftone screen frequency - e.g. FM screening, increase your solid ink density slightly (about 10 points), or switch to wider gamut process inks.
For comparison, here is an example of the larger 20 micron FM gamut (translucent) compared to 175 lpi GRACoL:



and here is the wide gamut Toyo Kaleido inks compared with GRACoL - both 175 lpi:



best gordo

[joe pasky]

Here's the 'white paper' the quote came from.

http://www.poynton.com/PDFs/Colour_interchange.pdf

[joe pasky]

Gordo:

Enjoyed your blog. I 'stole' your idea for the 'Live Feed'. Nice gadget.

joe

[joe pasky]

Great info...thanks to Eric and Gordo.

To the best of my knowledge, System Brunner is the only color monitoring and control system that measures, displays and calculates IFT moves with consideration for the the trap conditions you mentioned: halftone dots printing on bare paper at the highlights; partially overprinting at the midtone; and the majority of overprinting at the shadow.

However, this 'graying' from multiple internal reflections doesn't seem to be what the author was referring to.

The new G7 'how to...' suggests adjusting the gray balance scale, if necessary, to compensate for differences in paper color. (blue white vs. cream white). The basic approach 'automatically' accounts for MIR.

Your gamut plots seem to indicate that, as I suspected, the author is wrong in is assertion...or I am not understanding his point.

Am I correct in saying that the TOYO ink set is using very clean colors? or perhaps a Rhrodamine red? (I saw the brochures last year, and have long-since forgotten: old timer's disease)

What I'm trying to understand is how best to 'engineer' the entire workflow to take advantage of the wider gamut. It seems to me, for example, it makes no sense to have a wider gamut on press, if you compress it in photosphop by using a sRGB color space for the images.

So, what I'm thinking is that you need to shoot RAW when doing the photography or scan transparencies RGB with with a wide-gamut profile (Don Hutcheson posts one: donRGB.icc). On press you would need to use the G7 P2P target with the wide-gamut ink set to calibrate for a balanced gray-scale and correct tone curve. The thing I'm a bit unsure of is where to target the SIDs. I hear conflicting advice. TOYO says 20% higher than 'normal' density reading because their inks are more transparent. (anyone know if they are using a 'nano pigment dispersion' technique to achieve this?).

The next step would be to read the IT8 target from the 'characterization' run (after the CtP is calibrated for tone and balance). But, I'm fuzzy as to what do do with this profile.

cheers,
joe

[gordo]

My comments [GP] interwoven..
[JP] "However, this 'graying' from multiple internal reflections doesn't seem to be what the author was referring to."

[GP] Graying, or loss of chroma, does not come from "multiple internal reflections". It comes from light that reflects from the paper mixing with the light that has been filtered by the ink.

[JP] "The new G7 'how to...' suggests adjusting the gray balance scale, if necessary, to compensate for differences in paper color. (blue white vs. cream white). The basic approach 'automatically' accounts for MIR."

[GP] You can put a curve in a single color (C,M,or Y) to restore gray balance on paper that has a subtle difference in hue from neutrality. Typically this is done to the Y channel if possible since it's hard to see the tone distortion in the Yellow printer.

[JP] "Your gamut plots seem to indicate that, as I suspected, the author is wrong in is assertion...or I am not understanding his point."

[GP] The author's assertion is confusing because it's unclear whether he is comparing different printing gamuts to other printing gamuts or to CRT devices. He says "the nonlinearity of mixing produces a gamut for subtractive reproduction that is wider than would be the case for ideal, non-overlapping pigments." [GP the nonlinearity of mixing does not create a larger gamut] "The gamut of everyday printing inks, and everyday photographic dyes, extends beyond the CRT gamut in certain regions of color space." [GP that's correct, but again not related to nonlinearity]

[JP] "Am I correct in saying that the TOYO ink set is using very clean colors? or perhaps a Rhrodamine red?"

[GP] The use of Rhodamine red would not account for the extra gamut of Toyo Kaleido inks. Using Rhodamine red would just skew the gamut - and you could do this easily your self. ("Magenta" is a powerful gamut swing color. You can use anything from violet to warm red instead to compensate for CMYK gamut deficiencies - but other colors will suffer) This will be the subject of one of my personal blog posts LOL.

[JP] "It seems to me, for example, it makes no sense to have a wider gamut on press, if you compress it in photosphop by using a sRGB color space for the images."

[GP] Hopefully you wouldn't use sRGB for print :-)

[JP] "So, what I'm thinking is that you need to shoot RAW when doing the photography or scan transparencies RGB with with a wide-gamut profile (Don Hutcheson posts one: donRGB.icc)."

[GP] Adobe 1998 is already way larger than TOYO Kaleido - let alone conventional CMYK. I see no reason to use donRGB.
Here's a comparison. Adobe 1998 is translucent - TOYO Kaleido is opaque.



[JP] "On press you would need to use the G7 P2P target with the wide-gamut ink set to calibrate for a balanced gray-scale and correct tone curve."

[GP] You can use whatever technique that achieves the correct gray balance and tonality.

[JP] "The thing I'm a bit unsure of is where to target the SIDs. I hear conflicting advice. TOYO says 20% higher than 'normal' density reading because their inks are more transparent."

[GP] That makes no sense. If their inks are more transparent you will need to run a thicker ink film to achieve the same SID value. Maybe they mean running to a higher SID value?

[JP] "The next step would be to read the IT8 target from the 'characterization' run (after the CtP is calibrated for tone and balance). But, I'm fuzzy as to what do do with this profile."

[GP] I guess you'd create a separation profile to take advantage of the wider gamut.

best, gordo

[gordo]

Gordo: Enjoyed your blog. I 'stole' your idea for the 'Live Feed'. Nice gadget. joe

Thanks. Yes, indeed, a great blogger gadget. Nice seeing how people arrive at and from where they arrive one's blog site. But it would be nice if people left a comment as well. ;-)

best, gordo

[meddington]

Quick question Gordo...Why is the Gracol 175 lpi gamut plot different when plotted against FM compared to Toyo in your first post in this thread?