Cryptography Reference
In-Depth Information
• If β(S
CP=0
)≥β
∗
TH
+ 2, the meaning of the control pixel of S is
CF and its value is 0.
• Otherwise the meaning and the value of the control pixel depend
on the complexity, the adjacent pixel patterns and a bit to be
embedded into the control pixel. Table 8.1 shows the meaning
and the value in each case. In the table, b
n
means a bit of secret
data which is embedded into the control pixel.
Step 5) Replace noisy blocks with S.
Extraction
Following BPCS extraction steps, we can extract the blocks, which are denoted
by S
′
, containing the secret data by the complexity thresholding. All of S
′
can
be satisfied the following inequality about their complexity.
′
α(S
)≥α
TH
(8.18)
Basically, the embedded secret data is recovered from S
′
by the simple rule
described below.
• When the complexity of S
′
is less than or equal to 1−α
TH
, then the
control pixel means a bit of secret data. Thus all bits of S
′
are a part of
secret data.
• When the complexity S
′
is greater than 1−α
TH
, then the control pixel
means a conjugation flag. If the conjugation flag is equal to 1, then we
apply the conjugate operation to it. All the bits except for the control
pixel of the S
′
applied the conjugate operation are a part of secret data.
In order to take account of Table 8.1 used in the embedding procedure, in
addition, we need the exception rule described bellow.
′
• When the complexity of S
is equal to β
TH
or β
TH
+ 1, the control pixel
means CAB if the its value is equal to 1 and the adjacent pixel pattern
is BB.
• When the complexity of S
′
∗
TH
∗
TH
, the control pixel
means CAB if the its value is equal to 0 and the adjacent pixel pattern
is BB.
is equal to β
−1orβ
Embedded secret data can be recovered after the above steps are performed
for all blocks containing secret data.
8.4.3 Experimental Result and Discussions
We used the GIRL (256256, 8 bit/pixel) image as cover image. Noisy-
regions determined with m =8andα
TH
=46/112 were replaced with another
noisy pattern. We are unable to detect unnatural pattern from Fig. 8.11. in
