Cryptography Reference
In-Depth Information
Watermarked
frames
Correlation-value
calculation
BER
estimation
(
f
)
y'
Sorting
operation
Accumulation
control
Bit-value
determination
Bit
values
Fig. 7.10.
System structure of a statistically adaptive detection technique.
Correlation-value calculation: Calculates the correlation values from the re-
gion.
BER estimation: Estimates the BER from the correlation values of the region.
Sorting operation: Sorts the regions, which are the corresponding set of cor-
relation values by the corresponding BERs.
Accumulation control: Accumulates, one by one, regions that is sets of corre-
lation values in ascending order of their BERs, It re-estimates the BER
for the accumulated region at each step. The accumulated region having
the smallest BER is selected.
Bit-value determination: This determines the bit values. It is done by compar-
ing a threshold value with the set of correlation values of the accumulated
region and it selects the smallest BER.
The statistically adaptive technique can be applied to the various kinds of
correlation-based WM scheme described in Sect. 7.4.1.
Process Flow
The process flow of the statistically adaptive detection technique is shown in
Fig. 7.11. Step D3 represents the flows of the correlation-value calculation and
the BER estimation. Step D4 represents the flow of the sorting operation, and
Steps D5 through D7 represent the flow of the accumulation control. Step D8
represents the flow of the bit-value determination.
Step D1: Do the following steps over f
0
=1,F +1, 2F +1,.
Step D2: Input F watermarked frames y
′
(f )
s(f = f
0
,,f
0
+ F−1) and di-
vide FRK regions y
′
(f,r,k)
s(f = f
0
,,f
0
+F−1,r =1,,R,k =
1,,K).
Step D3: For each region y
′
(f,r)
≤f≤f
0
+ F−1, 1≤r≤R), calculate
the set consisting of the K correlation values,
(f
0
=c
(f,r)
k
c
(f,r)
1≤k≤K,
(7.21)
and estimate BER p(c
(f,r)
) from the set c
(f,r)
. The correlation value
c
(f,r)
k
′
(f,r,k)
of the region y
is given by correlating the WM pattern
with the region y
′
(f,r,k)
.Thatis,
m
(k)
