Re: Focoltone Question
Kyle,
You are correct to assume that a simple formula will not result in a match. I am not saying that modeling can not come close but it would be more complicated.
Some of the factors would be.
In your example, you have just one geometry of how the dots would be placed. The geometry changes as one moves from one point to another and this has an affect on the reflectance.
Also you have not accounted for mechanical dot gain. A 50% dot might have a mechanical dot size of 60%. This means that there would be less paper with no ink showing. This would reduce the paper reflectance component.
You assume that the dot has the same ink film thickness as a solid. As if the dot is a small solid. This is probably not so. Due to the ink spreading of the mechanical dot gain, the ink film probably is a bit thinner than the ink film of the solid. When you print ink at different ink films, this can change the hue of the reflected colour. Measure a solid and a screen printed with the same ink at the same SID and compare the a/b values. They will probably be different ratios. This is one reason printing the same ink on the same paper with FM and with AM results in problems in obtaining a match. The structure of the dot (ink film thickness) can have an affect on hue.
Then there is also optical dot gain which is the result of the drop in reflectance coming from the paper between the dots. The paper between the dots will not reflect the normal full amount of light that the paper would away from an ink film. This is due to the substrate being able to diffuse light internally.
In the overprinting of the dots there can be wet trap affects and also the possibility of the over print dot spreading more when printed on wet ink. I am not sure which has the bigger affect but it could be a factor.
So yes, a simple formula would not be very predictive.
The gamut question is not so clear to me. Since you are aiming at hitting a specific colour, the gamut size is not a factor. What I am guessing is that when you mix the C and M, this makes a special ink which if you want to print it lighter, then you print with a thinner ink film as opposed to the dots of C and M which you would have to reduce dot size. If you really want to make it much lighter, then you would have to add transparent white and then C and M only tint the ink.
At the extremes, where you want 100% C and 100% M from an ink mixture, I am guessing that the gamut is larger than the over printing of M on C due to the wet trapping loss of C.
Very interesting questions.
Erik