CMYK color model

CMYK (Cyan-Magenta-Yellow-blacK) is a model for specifying colors to be produced using subtractive processes, especially printing. This model utilizes the subtractive primaries cyan, magenta, yellow, and key black. According to theory, when cyan, magenta, and yellow are added together at full intensity, the resulting color is black. This works because cyan ink reflects all but red light, the yellow ink reflects all but blue light, and magenta ink reflects all but green light. In practice, a mixture of these three ink colors will not make a perfect black, but a dark gray. Therefore, black ink is included to aid in the reproduction of blacks and very dark colors.



Cartographic application
The CMYK color model is opposed to the additive primary color model, where when red, green, and blue are added together at full intensity the resulting color is white. When creating a map that will be displayed on a computer monitor the RGB color model is generally better to use. When creating a printed map it is generally better to use the CMYK color model. Computer monitors and other electronic visual displays utilize the additive color model. One problem that cartographers and printers deal with is the conversion between the RGB images displayed on their screen and the outputted CMYK images being printed out.

It should be noted that once a map is printed, the viewer can perceive the map colors differently due to the source of light and the color of the paper. The ink on printed maps absorb the wavelengths of the surrounding light; the light then reflected off the paper can produce different perceived colors than those on the computer screen. The cartographer has not control over the conditions in which the map is used or viewed. As such, it is suggested, and supported by research, that cartographers set CMYK values in increments of ten percent. Values over 40 percent should be set at increments of 15 to 20 percent. This will guarantee that the viewer can distinguish between colors in spite of the ambient light source.