CMY Pigments - Attaining Theoretical Curves

[Photo Engineer]

They can be simulated by both hand calculation and by computer simulation. They can also be simulated by blending dyes with different lambda max values (as shown in your reference - the cyan is double peaked). Although the light is purer, the amount of light transmitted is less. The overall effect, when compared to a "normal" dye is muddy, just as a narrow cutting dye is very pure and bright but looks surprisingly desaturated given equal density.

Light fastness and hue are always tradeoffs. The idea is to get both and that is done in modern films and papers.

PE

[holmburgers]

I see. So it really, truly is a balancing act.

Well then, is there any type of theoretical concept or technology that surpasses these considerations? Interference colors for instance, don't they behave in a totally different manner than dyes?

Signing off for the day. Ciao!

[holmburgers]

Here are some figures from Hunt's The Reproduction of Color.

1) The first graphs show the sensitivity curves for the cone's in our eyes.

How do you get the data for a graph such as the first one?; by "indirect" methods. Was Maxwell the first to investigate these values, or did Young & Helmholtz do any testing of their own?

Since each human has a somewhat unique response to color, what are the deviations from this mean? Wouldn't it be interesting to characterize sub-sets of color-vision, and then make photographs that would cater to each set? Imagine having 3 different prints, optimized for 3 (just as an example) different vision-types. Would these 3 people all prefer a different print?

2) The 2nd figure is a graph of the transmissions of CMY "dyes". Which dyes? This figure from the 2000 edition is no different than that from the 1950's edition; is it really the case that no progress has been made in attaining more "perfect" colors?

3) These are the retinal responses induced by the three CMY dyes. Notice how yellow is nearly perfect, magenta less so, and cyan quite lousy.

That is why the green & red separations (magenta & cyan respectively) must be masked to counteract these unwanted responses. In theory, each dye should only stimulate one of our cones.

Thinking this through aloud.... cyan should theoretically only absorb in the red, but it absorbs in the green to a great extent. In effect there is magenta intermixed with the cyan dye. Therefore a weak positive from the green filter separation is added in register to the red filter negative, subtracting the green densities from this layer.

Again, the magenta dye has unwanted absorption in the red (and to a lesser extent the blue) whereas it should only absorb green. The effect is having cyan intermixed (and yellow too). A positive is made from the red filter separation and registered with the green filter negative (and a lesser mask from the blue sep).

Have I got this right?

How do you determine the mask percentage? The area under the curve??

I appreciate the previous comments in this thread for sure, particularly about the importance of subjective evaluation, but I am hoping to gain a little more quantitative understanding of how color reproduction works.

TGIF!

[Photo Engineer]

As Bob says in his book, these curves for the eye were obtained indirectly, but they are a fair representation. As for your second figure, these are drawn "upside down" from general practice their being transmission curves instead of density.

For more information on a variety of "modern" dye sets see my thread on Kodachrome, a love hate relationship. In it, I mention the different human responses to dye sets based on variations in human vision.

I should add that I took my first extensive course from Bob and a fellow scientist of his who cam to Kodak Park to give the course to some newbies (like me) way back in the late 60s. In June 2009, Bob gave an invited lecture at RIT on color science. He then went to GEH and had lunch with our group. The occasion was his being granted the title of Sir Robert Hunt OBE by Her Majesty, Queen Elizabeth II.

PE

[holmburgers]

Thanks Ron, I do recall that discussion about different eye responses. That was in the back of my head while writing this.

More specifically, my thinking is that the sensitivity curves must be the average of many people, right? But what if we tested a million people and instead of averaging the whole population into one curve, we find several groups that show a statistical significance to one another in the way that they skew from the mean. Does that make any sense?

So we have X number of groups, and the members within a group see things similarly, but different from the other groups. There will of course be the median population, but maybe there are groups of outliers that have never seen a print really pop for them.

Anyways, this is kind of a tangent. I'm really interested in why there hasn't been much progress in reducing unwanted absorptions in CMY dye sets. This seems independent of the narrow/wide band discussion above.

I recall seeing a headline on ScienceDaily.com once that "Scientists Discover Blackest Black", and well, I'm waiting for "Scientists Discover Magentaist Magenta".

[Photo Engineer]

Magenta is not a color!

Actually, the human response can be derived from extracting the dye "sensitizers" from the eyes of cadavers. That is, if you insist on knowing how it is done. Then the researcher can also compare this to light reflected from a living eye by shining light into the eye in narrow beams and recording what comes back. So, there are two sources to derive families of sensitivity.

What we find is that many like one color over another based on the family of dyes in the eye. This is a very rough statement as color is subjective as well. In the end, we have to average.

As for improving dyes, well it has been done over the years. The current magenta is quite improved over that of 70 years ago in both hue and stability, but azomethine dyes have this property of having unwanted absorptions due to resonance effects. So, a cyan has some blue and lots of red absorption, and it always will.

PE

[holmburgers]

Ahah! That's the kind of info I was looking for!

And right, sorry.... "Scientists Discover Complete Opposite of Green".

Well, tell me more about these resonance effects. This sounds interesting. What conditions would have to exist to eliminate these problems, and are there any super cutting edge sciences that might be able to address these problems?

Again, I'm thinking nanotechnology. Afterall, that's where the colors are made.. in the nano's...

Ok, it's weekend time... enjoy yourself Ron.

[Photo Engineer]

An azomethine dye is fundamentally made from a C=N chromophore whereas an azo dye is made from an N=N chromophore. These two dye classes have different spectra comparing dyes with the same lambda max. Basically, the azo dye will generally have less unwanted absorption.

Drawing the different forms of the molecule is difficult and will not "prove" anything to anyone and the math is quite esoteric and not my field. This is a job for a physical chemist to explain and understand, so it will be meaningless here as well. Sorry.

The bottom line is that we have apples and oranges and they behave differently as you can see if you compare spectra.

Unfortunately, I have no spectra for you to compare. Ideally, Ilfochrome dyes should be compared to Endura or Crystal Archive papers for a proper understanding of this topic. Kodak has published the Endura dyes, but a search for the Ilfochrome spectra came up with nothing.

PE