HP PCL/PJL reference (PCL 5 Color) - Technical Reference Manual

1-4 Color Printing Overview EN
Color can be described in ways other than amounts of red, green, and
blue light. Generally, these color specification systems are known as
color spaces. For example, The Cyan, Magenta, Yellow (CMY) color
space is used to describe colors that are printed by depositing varying
amounts of these three ink pigments (Cyan, Magenta, Yellow). The
absence of pigment is considered to be white, and the presence of all
three is black. The CMYK color space is similar to the CMY color
space, but black pigment is used in place of 100% C, M, Y since
imperfections in the hues of the C, M, Y pigments yield a dark brown
rather than black.
A color specification, then, depends on the color space as well as the
values used to describe a given color. Black in the RGB color space is
described using the three numbers (0, 0, 0), but in the CMY color
space it is described as (100, 100, 100), where the values are
percentages of each color.
Color Management and the Standard Red,
Green, Blue Color Space
For color to be reproduced in a predictable manner across different
devices and materials, it has to be described in a way that is
independent of the specific mechanisms and materials used to
produce it. For instance, color displays and color printers use very
different mechanisms for producing color. Traditionally, operating
systems have supported color by declaring support for a particular
color space (RGB in most cases). However, since the interpretation of
RGB values varies between devices, color was not reliably
reproduced across different devices.
The needs of the very high-end publishing sector could not be met by
the traditional means of color support, so the various computer
operating systems added support for using International Color
Consortium (ICC) profiles to characterize device-dependent colors in
a device-independent way. They used the profiles of the input device
that created an image, and the output device that displayed or printed
the image, to create a transform that moved the image from the color
space of the input device to that of the output device. This resulted in
very accurate color and access to the entire color gamut of both
devices. However, it also involved the overhead of transporting the
profile of the input device with the image and running the image
through the transform.