The creation of colors by combining various colored inks on a white piece of paper is quite different. Here the observed color is the result of reflected light, and each color of pigment placed on the paper absorbs certain colors of light. This is a subtractive system, and uses cyan, magenta, and yellow pigments, which are complementary to the additive red, green, and blue of the computer screen. These colors may also be measured on a scale of 0 to 1, and are related to the computer's red, green, and blue by the formulae: CYAN = 1 - RED; MAGENTA = 1 - GREEN; and YELLOW = 1 - BLUE. Using no pigment leaves the paper white, while maximum pigment of all three colors produces black.
Although images are reduced to RGB components
to display on the computer, and to CMY for printing, another parametrization
is more appropriate to establish a correspondence with the complex numbers.
In the Hue, Saturation, Value, or HSV color scheme,
the parameter Hue is an angle measuring position around the color
wheel. Red has a Hue of 0 or 360 degrees; green has Hue
120 degrees, and blue has Hue 240 degrees. Yellow has Hue
60 degrees, half way between red and green. A Hue of 30 degrees
corresponds to orange, etc. A 'pure' red or green or orange can be
mixed with white to create a pastel shade. As more and more white
is mixed in, the original Hue becomes indiscernible. The parameter
Saturation
measures how far a color is from a white or gray toward a 'pure' color.
When Saturation is zero, the color is white, gray or black.
When Saturation is one, the color is 'pure' with no white mixed
in. 'Pure' colors are composed of at most two of the primary colors
red, green, and blue. The parameter Value is also measured
on a scale of 0 to 1. Decreasing Value is like turning down
the brightness control on a television set or computer monitor. Value
zero gives black, no matter what hue and saturation are.