Three-Dimensional Control of Color Management Systems - Control of Color Imaging Systems: Analysis and Design - page 363

FIGURE 7.40 (See color insert following page 428.) Image showing the rendering of
color sweeps with ICC profile from Example 7.8 (left: original image; middle: MM inversion;
right: control-based inversion).

CMYK color space, C þ M þ Y þ K would be constrained to be less than a thresh-
old. A second constraint is to maintain K between certain minimum and maximum
values. In Refs. [82,83], another UCR GCR strategy is proposed in which the

optimization is done to reduce moiré. In this method, the UCR

=

GCR strategy is
used to characterize the moiré as a function of the color components and to select
the optimized output color components when the moiré function is minimized. In
another method, Ref. [87], a

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flexible method for estimating the black component
comprises (1) determining maximum black component, (2) adjusting the black
component amounts based on chroma, and (3) determining the other color com-
ponents. But this method has a disadvantage of not producing suf ciently opti-

mized colors for the entire color gamut.
Various other GCR control strategies are shown in [84 - 86]. In the Pareto-
optimal approach [101,102] ICC-based pro le LUTs are built to convert images to

CMYK, and consistency (i.e., a colorimetric accuracy match) is introduced through
carefully selected optimization parameters that attempt to use unique CMYK solu-
tions during the inversion process and yet preserve arbitrary GCR

flexibility within a

printer s reproducible limits. Although the Pareto-optimal approach, one of the more

'

flexible GCR methods, provides good control of multiple GCR schemes with full
CMYK gamut utilization and a controlled substitution of black into a single meth-
odology, it can lead to loss of accuracy during inversion. Other inversion methods
are shown in Ref. [103] to generate ICC pro

le, and in Ref. [104] generate LUTs to

minimize metameric effects.

7.5.4 GCR C ONSTRAINED 4- TO -3 I NVERSE
The CMY gamut (referred to as the gamut with K not equal to zero and with CMY to
CMYK GCR) is generally limited by the type of GCR function used as compared to
the full CMYK gamut. Due to this limitation, the designer should be cognizant of