The CMY color space describes colors in terms of the subtractive
primaries: cyan, magenta, and yellow. CMY is used mainly for hardcopy
devices such as color printers. Generally, the conversion from
RGB to CMY follows the equation :
A related color space, CMYK, uses a fourth channel (K) to represent black. Since conversion to CMYK requires a min() operation, it cannot be performed using the color matrix.
The extension EXT_CMYKA also supports conversion to and from CMYK and CMYKA. This extension is currently supported by Evans & Sutherland.