HP RIP Software - HP RIP Software User Guide

4-4 Color Management Overview
varies the hue. Upwards movement from one disk to another increases
the lightness. Radial movement from the center of each disk outwards
increases saturation. The model is irregularly shaped because the eye
is more sensitive to some colors than to others.
Colors on your monitor need to be reproduced by printing ink on paper.
Spot colors are reproduced with pre-mixed inks, while process colors,
such as the Standard Web Offset Press set (SWOP), are reproduced
with cyan, magenta, yellow, and black inks (CMYK). Spot color inks (for
example, the PANTONE Matching System) provide a much larger color
gamut than CMYK process inks used by ink jet printers and offset
presses.
The CIE Yxy Color Model
In 1931 the “Commission Internationale de l’Eclairage” (CIE) precisely
defined three primary colors, or tristimulus values, called X (red), Y
(green) and Z (blue) from which all other colors visible to a “standard”
observer could be created. This is the XYZ model.
Another space to represent colors is the CIE Yxy color model. In this
model, all colors having the same lightness lie on a roughly triangular
flat plane. This is the color space shown at the end of the color profile
creation process.
The CIE L*a*b* Color Model
The non-linear CIE Yxy color model was mathematically transformed in
1976 to the uniform CIE L*a*b* model, in which distances between col-
ors more closely match those perceived. All colors of the same light-
ness lie on a circular flat plane, across which are the a* and b* axes.
Positive a* values are reddish, negative a* values are greenish, positive