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Device-
Independent
Color
The PCL language characterizes color as either device-de-
pendent or device-independent. Both categories encompass
many color spaces, each with unique characteristics.
Device-
Dependent
Color
Device-dependent color is relative to the device’s inherent
characteristics. For example, the colors produced by
plotters are relative to the color of the installed plotter
pens. Pen color varies considerably, especially as pens wear
out, changing the color of the output. Likewise, for monitor
screens, the red, green, and blue screen phosphors
determine the colors produced. Fully saturated colors can
vary greatly between screens. For printers, the color
produced on a page depends on the printer’s subtractive
inks or toner (cyan, magenta, yellow, and black).
When using device-dependent color, devices receiving
relative color specifications for the same color frequently do
not produce the same color. For example, a monitor’s
saturated red may be different than a plotter’s. In short,
the same color page may appear considerably different on
different devices.
The HP color printers provide device-dependent color
specified using either the Device RGB or CMY color spaces.
Device-
Independent
Color
In contrast with device-dependent color, device-independent
color is based on an absolute color standard—the
tristimulus values of human vision. The device, whether a
printer or otherwise, is calibrated to match an independent
color specification. The color specification is translated in
such a way that the resultant color is independent of the
device. Examples of color spaces based on absolute
standards include Kodak Photo YCC, CIE L*a*b*, YUV, and
the proposed YCrCb. Each is a transform from tristimulus
CIE XYZ space.
With proper calibration, any device can provide a transform
from device-independent color space to the device’s own
color space, producing output from different devices that
have the same color appearance. For example, if a monitor’s
Color Printing Overview 1-9Color Printing Overview 1-9