Image Processing Reference
In-Depth Information
CYK
MYK
CMK
FIGURE 7.49
Top view with CMK, MYK, and CYK gamuts.
yet another zero black tricolor (CMY) gamut class. It overlaps with other classes that
include the K separation. While using this GCR, the node colors have to be carefully
assigned to one of the CMK, CYK, or MYK gamuts and the overlapping CMY
gamut should be avoided. Otherwise, it can lead to severe formulation jumps and
discontinuities unless some form of iterative blending is introduced. The overlap
region with the CMK, CYK, and MYK gamuts are generally nonexistent except for
numerical precision. Whenever there is an overlap with a CMY gamut class, this
strategy has two components: (1) minimum black strategy and (2) maximum black
strategy. For maximum black strategy, use black everywhere (i.e., no CMY gamut)
including neutrals (Figure 7.50). Minimum black strategy would not work for images
due to discontinuities or abrupt changes in separations, as seen in the CMYK
response for the colors on the neutral axis from C
¼
M
¼
Y
¼
K
¼
0toK
¼
255
corner (C
¼
M
¼
Y
¼
255) (Figure 7.51). Whereas, for rendering spot
colors, a minimum black strategy with CMY gamut class can be used without
worrying about discontinuities.
A smooth GCR can be obtained for a minimum black strategy by using the steps
of Example 7.9 (multidimensional
0 and K
¼
filtering and control-based iterations multiple
times) of a four tricolor gamut class GCR [109,110] (i.e., CMY, CMK, MYK, and
CYK). The blended GCR response is shown in Figure 7.52.
7.5.5 GCR R
ETRIEVAL FROM
H
ISTORICAL
P
ROFILES
In this work
or in digital front end (DFEs), the
documents are designed using various layout tools and their color appearance is
ow, particularly in the prepress and
=
ne
tuned by typically proo
ng on a workgroup digital printer or the press itself. When
the prints are made, it is expected that the appearance on the destination printer
follows the proof. If it does not follow the proof, then adjustments are made in many
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