Just to try, a mixed color synthesis process

by adrien

grey sample adrien lucca plotter june 2013

A grey color sample in mixed additive/subtractive color synthesis


You might have heard of the “additive” and “subtractive” color syntheses at school or anywhere else before.

When I was an art student, the difference between the two syntheses of color was explained to me in terms of difference between “material colors” and “colored lights.” The two canonical examples were the computer screen’s RGB and the offset CMYK color systems.

I have never been satisfied by these explanations and examples. My fist-ever counter-argument was simple: a screen and an object under a light source both emit light in the direction of my eye, so why make a difference between two types of objects that both emit light?


How I abandoned subtractive colors

Since then, I have been trying to create a (material-) color process that would be as easy and as precise as the union of an image editor and of a computer’s screen, but on paper (see my series D65 studies, 2011-2013.)

In 2009, I decided to abandon the use of any transparent colored material (inks, watercolors, etc.) because there was for me no precise way to control the amount of material that I would put on the paper: if you put more ink it makes a thick layer when it dries, which appears darker than a thin layer.

Also, transparent inks produce quite unpredictable colors when you superimpose them…

Color averages (additive color) on paper

To control additive color synthesis is a much simpler process: imagine yourself with a piece of white paper and a opaque black paint, if you can cover almost exactly 1/2 of the paper with small black dots, black lines, a checkerboard or anything that diffuses evenly enough the black on the paper, the resulting color of this object – optically – will be in-between black and white, namely a grey optically made of 1/2 of these white and black materials.

Such a mixture has a simple meaning, but how would you find a 1:1 mixture of black and white if you were mixing paints? What would 1:1 mean? Without a model of human vision, nothing.

grey detail

Magnified view of the 1st picture : it’s hard to see but there are 8 colors

Combining addition and subtraction

The advantage of using opaque colors was the easiness of creating an additive color process on paper (making color averages.) However, if we possess a tool that can pour on paper transparent colors evenly, we can include the transparency of the colors in the process. A true mixed process is then created, with 3 primaries on white, we get 8 colors already.

Of course, this is not any different than the traditional quadri offset process!

model mixed color synthesis

If we already measured the colors resulting when superimposing the primaries, we can predict the appearance of such color-mixtures with basic equations, where 3 variables x, y, z, refer to the amounts of the 3 primaries (tartrazine yellow, quinacridone magenta, phtalocyanine cyan)

However, it seems quite unstable for now and much harder to calibrate than my previous additive process.