Image Processing Reference
In-Depth Information
FIGURE 9.24
Circular cyan sweeps through (a) identity reference TRC, (b) reference TRC 2,
and (c) reference TRC 3. No printer model is involved in this simulation.
FIGURE 9.25
Circular cyan sweeps through the printer model without any inversion.
shown in Figure 9.25. Figure 9.26 contains images with and without level 3
compensation. Images shown on the right are processed through level 3 TRCs
and the printer model. They show matching with corresponding
figures in Figure
9.24, as expected by the TRC linearization process.
9.9.2 C
ONTROL
-B
ASED
TRC I
NVERSION
P
ROCESS
A control-based TRC inversion process is made possible via a state-space represen-
tation of the tone reproduction at each of the measurement patch area coverages. If
the gradient of the tone curve at each of these patch area coverages is known, then a
state-space model with an integrator in the control loop can be written as follows:
x
(
k
þ
) ¼
Ax
(
k
) þ
Bv
(
k
)
y
(
k
) ¼
Cx
(
k
) þ
Dv
(
k
)
1
(
9
:
48
)
2
3
2
3
x
1
(
k
)
x
2
(
k
)
:
:
x
N
(
k
)
D
U
1
(
k
)
D
U
2
(
k
)
:
:
D
U
N
(
k
)
4
5
4
5
where x
(
k
) ¼
, v
(
k
) ¼
, y
(
k
) ¼
x
(
k
)
, A
¼
I, B
¼
J, C
¼
I, and
D
¼
0. The controller uses a gain matrix and an integrator modeled by the following
equation (Section 9.2):
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