Additive Color Mixing
Our human color vision is based on three types of cones: three receivers. We have essentially red, green, and blue channels. Because of this physical characteristic, it is possible to mix different wavelengths of energy (or colors) to create what appears to be white light. We begin with black - - no light and ADD light moving in the direction of white. To do this we ADD equal amounts of red, green, and blue. We can mix these same additive primaries in various proportions to produce (virtually) any color. A color television, computer monitor, or stage lighting all demonstrate the additive color process. Three beams of light projected through red, green and blue filters illustrate how these additive mixtures react.
By superimposing two primary colors, a secondary color is created. For example, when red and green lights are superimposed, yellow is created (the absence of blue); green and blue creates cyan (the absence of red); blue and red creates magenta (the absence of green).
Subtractive Color Mixing
The subtractive process reverses the scenario above. Here we start with white and add pigments or dyes to selectively absorb light energy (we subtract from white). Any material containing pigments or dyes will selectively reflect, or absorb light energy across the visible spectrum. In the case of transparent objects, light is either absorbed or allowed to pass through.
Subtractive color mixing is used in the printing industry and is called “four-color process”: three subtractive primaries, Cyan [C], Magenta [M], and Yellow [Y], plus Black [K] (also known as “process colors”). Black ink is added to achieve a deeper black than could be made by mixing the three primaries. In addition, the black ink is much less expensive and can be used to substitute where overprints of all three primaries occur. In the Graphic Arts workflow, original images are “separated” into layers that represent their amounts of Yellow, Magenta, and Cyan. The images are broken down (screened) into thousands or millions of dots. In analog or conventional printing, these dots vary in size according to the amount of color that existed in the original. In digital or stochastic screening, the dots remain very small but vary in number. The separated image is burned onto plates which then are mounted onto the press. Using the process inks, the printing press “reassembles” the original image from the dots on a paper or other (typically white) substrate: a full range of color can be achieved.
Subtractive primaries are complimentary to additive primaries. For example, a Yellow absorbs Blue energy and reflects both Red and Green. Cyan subtracts the Red and reflects both Green and Blue, and Magenta subtracts Green reflecting both Red and Blue. Collectively the three subtractive primaries absorb the entire visible spectrum. By combining all three subtractive primary colors, the resulting image appears black since all light is absorbed.