Cryptography Reference
In-Depth Information
D
cb
=⌊log
2
Q⌋. (5.9)
According to the embedding capacity D
cb
, we are able to embed D
cb
secret
bits into the image data. An example of how D
cb
is derived and how the
embedding method works is shown in Fig. 5.9. This uses the result of the
example in Fig. 5.7(d). That is, D
cb
is calculated using Eq. (5.8) and Eq. (5.9).
D
cb
is 20
1
. Then, a bit stream with 20 secret bits is used in the secret data A
is embedded in this cover image. Assume a bit stream with 20 secret bits that
is transformed to a corresponding unsigned integer to become 916667. The
clusters, S
1
, S
1
, S
2
, S
3
, S
1
, S
1
, S
2
, S
1
, S
1
, S
3
, S
3
,andS
2
, to which the colors
belong, are selected in order to produce the combinations of the elements.
In Fig. 5.9(a) the final combination result is the 916667-th combination. The
Stego-Image is shown in Fig. 5.9(b).
Fig. 5.9.
An example of the combination technique.
5.3.2 The Extraction Procedure
The extraction procedure is used to extract the secret data from the Stego-
Image. The extraction procedure in the traversing order is similar to that in
the embedding procedure. For all of the embeddable image data X,weextract
the secret bit when
f (c
X(i,j)
)
= 1. The product data Q is calculated when
1
D
cb
=⌊log
2
(3342313114333341)⌋=
⌊log
2
1259712⌋=20
