The Language of Additive and Subtractive Color Mixing
by Joseph N. Tawil

Few subjects are more difficult to articulate than color. Describing colors and color mixing systems is a minefield of linguistic problems, not the least of which is the confusion between ADDITIVE and SUBTRACTIVE color mixing. The purpose of this article is to lend clarification and understanding about the language employed that describes these two color mixing theories.

Additive Color Mixing

Color mixing with light is called ADDITIVE Color Mixing. This tri-color mixing theory was proposed by Sir Thomas Young in the early 1800's and it is the basis for all film and video color systems today. Young discovered that by mixing red, blue and green light he could make most of the colors in the visible spectrum. Young determined that red, green and blue were the ideal primary colors of light because they allow for the widest variety and create a reasonable "white". Red, green and blue are three colors which are widely separated from each other and because of this they will combine to make many other colors including in the right circumstances, "white".

Combining any two primary colors creates a secondary color which is a complement of the third primary (complement as in completes). For example, by combining red and blue you get magenta and other colors in the violet and pink range. Combining blue and green generates cyan (blue-green) colors. Combining red and green creates yellow and other colors in the orange range.

Complementary colors are also called secondary colors. Violets and pinks are complementary to the primary color green because they contain red and blue. Oranges and yellows are complementary to the primary color blue because they contain red and green. Tri-color mixing is illustrated in Chart I. It is interesting to note that the complementary colors (or secondary colors) created in the ADDITIVE color mixing process cyan, yellow and magenta, are the primary colors of the SUBTRACTIVE color mixing system. Obviously, this is not an accident and the two theories do tie together.

SUBTRACTIVE COLOR FILTERS

SUBTRACTIVE color filtering is something all of us have experienced in elementary school, where we have mixed paints to make a variety of colors. Later on we probably read some art books where painters talked about mixing primaries to make different colors. The primaries are often described in these art books as red, yellow and blue. Film makers however see the SUBTRACTIVE color mixing primaries described as yellow, cyan, and magenta. Using the same language to describe primary colors in both the SUBTRACTIVE and ADDITIVE color mixing process causes a great deal of confusion. Printers and film makers define the SUBTRACTIVE primary colors more accurately as cyan, yellow and magenta (CYM) separating them from the ADDITIVE color process. In SUBTRACTIVE color mixing as we mix the primary colors of paints, inks (or filter emulsion layers) the resulting color is darker and darker and eventually black.

In order to be visible an object must give off light. The object might be an actual light source or a reflective light source. Objects that do not produce light are colored by a "color subtraction" process. When "white" light strikes the object some colors are absorbed and others are reflected. Pigments, paints, dyes and inks make color by subtracting a part of the visible spectrum. The process is known as SUBTRACTIVE color mixing.

The color mixing charts shown above illustrate the two sets of "terms" used to describe SUBTRACTIVE color mixing. The confusion created by borrowing the same language of ADDITIVE color mixing (Illustration II) was corrected by adopting the more specific color descriptions, cyan, yellow and magenta (CYM) (Illustration III). Printers and professionals dealing with color mixing use these names (CYM) so as not to confuse ADDITIVE and SUBTRACTIVE color systems. The term CYMK might also be familiar. In the four color printing process the K represents black. In the film process CYM is used to describe the layers of color emulsions which give us our color photography.

Describing the Color of Light (ADDITIVE)

Hue, Value and Chroma are terms from the Munsel system of color notation (1905) a system designed for describing color in ink and paint rather than the color of light. However, Munsel¹s three descriptive terms are often used to define the color of light contributing more to the confusion than the clarity of the subject. The vocabulary of color tends to become a minefield of contradictions and confused meanings. Colorimetry is another system for describing color which is of importance because it relates well to describing colored light. In colorimetry the following terms are used to describe the color of light: Dominant Wavelength (DWL), Brightness and Purity. DOMINANT WAVELENGTH: The apparent color of light similar to the term hue meaning the apparent color i.e. red, blue. BRIGHTNESS: The percentage of transmission of the full spectrum of energy (similar to value) and often described as intensity. PURITY: Similar to chroma in that it describes the mixture of color of the DWL with white, or the color of the light source. If there is only the color of the DWL, it is 100% pure. If there is very little of the DWL in the mixture, (as in a tint) the color would be say 5% pure. BLACK: The absence of all colors. WHITE: The presence of all colors.

Describing the Color of an Object (SUBTRACTIVE)

Color descriptions for an object are usually dominated by the Munsel system of color notation which popularized certain terms. Hue, value and chroma have become the most frequently used terms for color description. As useful as these terms are, it leaves out one very valuable characteristic, Texture. HUE: Color or color family i.e. red, green blue and yellow. VALUE: The intensity of a color as it is compared to the lightest to the darkest as it ranges from white to black. CHROMA: Saturation or purity of a color from its most vivid pure to its lightest tint. TEXTURE: The surface properties of a color as in shiny or matte, reflective or diffusing.

You can see from these two sets of definitions the terms have somewhat similar meanings but not exactly the same. They can often be confusing when descriptions of the color of an object (SUBTRACTIVE) are used to describe the color of light (ADDITIVE). This is a linguistic problem, not a color theory problem. One set of descriptions is appropriate to describe light or the result of ADDITIVE color mixing. The other is appropriate to describe the color of an object SUBTRACTIVE color mixing.

Summary and Conclusion

We have reviewed the two theories of color, ADDITIVE and SUBTRACTIVE color mixing. We have noted that the primary colors are different for these two systems. ADDITIVE color mixing uses red, green and blue (RGB). SUBTRACTIVE color mixing uses cyan, yellow and magenta (CYM). The primary colors in the SUBTRACTIVE coloring system are the secondaries of the ADDITIVE color mixing system. These two systems of color mixing are the basis of all film and video color production.