Image Processing Reference
In-Depth Information
FIGURE 8.28 (See color insert following page 428.)
Top view of CMK, MYK, CYK
gamuts and neutral zone (CMY gamut removed from the figure).
model of the type described in Section 7.4. There is a high degree of overlap
between the CMY gamut with other classes that include the K separation. The
overlap of the CMY gamut with the CMK, CYK, and MYK gamuts can cause
problems while assigning spot colors to appropriate gamut classes. Whereas
the overlap region of the CMK, CYK, and MYK gamuts is low. Figure 8.28
shows the CMK, MYK, and CYK gamuts along the chromatic axes when viewed
from the top of the gamut.
To reduce the overlap with the CMY gamut class and to preserve the appearance of
images, the neutral zone (region) is de
D
E metrics. In some cases, this
neutral zone may not be needed. This zone, as shown in Figure 8.27c and d, geomet-
rically looks like a cylinder of circular cross section in 3-D space when the cylinder is
speci
ned using the
D
E
a
*
as a radius from the neutral axis. It is much less cylindrical when
the radius is speci
ed with
ed in
D
E
2000
or perceptual space. A classi
cation algorithm is
shown in Ref. [12].
Whenever there is overlap with the CMY gamut class, at a high level, this strategy
has two components: (1) minimum black strategy and (2) maximum black strategy.
For minimum black strategy, we use the CMY gamut class wherever possible. For
maximum black strategy, we use black everywhere (i.e., no CMY gamut is used).
The use of tricolor gamut classi
cation algorithm removes the degeneracy while
c terms, it reduces the dimensionality of the
four-color process to three-color groups. In summary, this approach provides (a)
improved spot-color accuracy with one of the separations always held to zero,
(b) improved toner usage for high area-coverage spot-color printing by identifying
the most toner ef
finding the CMYK recipes. In speci
cient CMYK values for each spot color, (c) more room for the
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