Image Processing Reference
In-Depth Information
ray-based control model described in Section 7.6.1 to separate the colors into
two groups. These colors are the nodes in L*a*b* space at which the device
CMYK values are found that populate the multidimensional CLUT of the ICC
pro
le. The RGB and the corresponding L*a*b* node values are shown in
Table 7.15 for in-gamut colors. The out-of-gamut nodes are shown in Tables
7.16 and 7.17.
Step 4:
Perform gamut mapping for out-of-gamut colors.
In this example, we used a simple centroid clipping (Section 7.6.2, Figure 7.57)
with ray-based control model. The gamut-mapped L*a*b* and their corresponding
CMYK values are shown in Tables 7.16 and 7.17. Clearly, all of the out-of-gamut
nodes are mapped to the gamut boundary.
Step 5:
Perform constrained GCR inversion for in-gamut colors.
We used the K-restricted GCR method during the inversion process. Table 7.15
contains the CMYK values corresponding to each in-gamut node. Now rearrange the
in-gamut and out-of-gamut RGB to CMYK LUTs to form a single LUT with color
index incremented from 1 to 216. To create an ICC pro
le, this LUT can be used to
fill the CLUT inside the ICC structure.
TABLE 7.15
RGB ! L*a*b*andL*a*b* ! CMYK LUT for In-Gamut Node Colors
Node L
*
a
*
b
*
(Out-of-Gamut Colors)
RGB Values
GCR Constrained CMYK
Color
Index
L
*
a
*
b
*
R
G
B
C MY
K
44
51
51
51
28.16
0.00
0.00
111
80
85
182
45
51
51
102
28.17
4.98
39.26
207
142
12
92
50
51
102
51
46.00
56.96
30.76
221
9
246
21
51
51
102
102
46.00
52.85
8.51
227
14
145
17
80
102
51
51
36.86
48.31
15.00
6
218
105
110
81
102
51
102
36.87
50.72
24.27
101
216
4
25
86
102
102
51
50.94
2.24
39.27
107
88
209
55
87
102
102
102
50.94
0.00
0.00
137
105
107
28
88
102
102
153
50.94
3.31
31.78
155
102
27
11
122
153
102
51
57.24
39.55
50.12
21
160
206
18
123
153
102
102
57.24
41.01
10.86
39
154
89
12
20.93
124
153
102
153
57.24
43.19
61
151
4
1
3.46
128
153
153
51
69.38
71.05
62
46
229
20
129
153
153
102
69.38
2.07
31.79
80
67
141
5
130
153
153
153
69.38
0.00
0.00
96
72
73
2
170
204
204
51
85.46
4.38
98.79
20
14
249
14
171
204
204
102
85.46
3.40
59.52
30
30
162
4
172
204
204
153
85.46
1.92
27.73
38
33
94
2
173
204
204
204
85.46
0.00
0.00
51
32
33
3
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