I've derived theoretical C, M and Y plates from the RGB channels in the previous entry on Additive Color Mixing.
To achieve the cyan plate, I took the red channel, negated it, multiplied it by full (255 0 0), then inverted (color negated) the result. I did the analogous steps with the green and blue channels to derive theoretical magenta and yellow color plates.
The blend mode between each derived color plate is MULTIPLY.
The layered .psd file is here if you'd like a closer look.
Now lets simplify the Photoshop file. I merge the layers in sets of 3 starting from the top so that we can get a plain look at these theoretical CMY plates.
Cyan, Magenta and Yellow color ink plates on white paper - with a multiply blend mode between each.
Here is the layered .psd file if you'd like a closer look.
So what is with this 'theoretical' word, anyway? And why only CMY? Where is the K?
Good questions. I'll try Photoshop-produced CMYK plates next...
UPDATE 6/1/2009
Actually CMY is not just theoretical, now that I think about it. Color motion picture film is 'subtractive' CMY - no K. So this mimics the behavior of color motion picture film.
Here is another variation on the Photoshop file.
Subtractive-Color.psd
By replacing the C, M, or Y 'emulsions' with faded, dirty, warped, misaligned or scratched versions I could mimic an aging film effect fairly well.
UPDATE 6/4/2009
A good description of the process of colorizing and assembling three black and white color separations. [pdf] I think today's Photoshop may automate the registration/alignment process better now.
UPDATE 6/15/2009
An in depth look at the linear equations and non-linear lookup tables that more closely approximate the RGB to CMY conversion can be found in Digital Color Halftoning by Henry R. Kang
Leave a comment