Cryptography Reference
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(a) (b) (c) (d) (e) (f)
(g) (h) (i) (j) (k) (l)
Fig. 11.14.
Watermarks extracted from spatial-domain-attacked watermarked im-
ages. (a) The robust one from Fig. 11.13(a), NHS = 0.887. (b) The semi-fragile one
from Fig. 11.13(a), NHS = 0.901. (c) The robust one from Fig. 11.13(b), NHS =
0.868. (d) The semi-fragile one from Fig. 11.13(b), NHS = 0.164. (e) The robust one
from Fig. 11.13(c), NHS = 0.954. (f) The semi-fragile one from Fig. 11.13(c), NHS
= 0.645. (g) The robust one from Fig. 11.13(d), NHS = 0.647. (h) The semi-fragile
one from Fig. 11.13(d), NHS = 0.103. (i) The robust one from Fig. 11.13(e), NHS =
0.926. (j) The semi-fragile one from Fig. 11.13(e), NHS = 0.245. (k) The robust one
from Fig. 11.13(f), NHS = 0.710. (l) The semi-fragile one from Fig. 11.13(f), NHS
= 0.035.
Fig. 11.15. The extracted watermarks are shown in Fig. 11.16. From these re-
sults, we demonstrate the robustness of the robust watermark and the fragility
of the semi-fragile watermark to rotation.
In order to show the effectiveness of the proposed algorithm for other im-
ages using the watermarks above, we do the similar experiments based on the
other two test images. That is the Pepper and F16 images. The experimental
results are shown in Table 11.1, where the rotation angles are 0.5
◦
◦
. This
is done in order to show the robustness of the proposed algorithm to rotation
operations. For the cover images, the product Codebook C
1
has a size of 16
for Stage 1, and the Codebook C
2
has a size of 256 for Stage 2. The codebook
used in the watermarking algorithm is the same as Codebook 1 used in VQ
compression attacks. This is trained from the cover image. The Codebook 2
has a size of 8192 and the Codebook 3 has a size of 256. The Codebooks 2
and 3 used in VQ compression attacks are trained from the cover image itself.
The Codebook 4 has a size of 4096 used in VQ compression attacks is trained
from the Lena image. The parameters of the spatial-domain attacks are the
same as that in Lena image watermarking.
and 3
11.2.4 Conclusions
An e
cient multipurpose watermarking algorithm based on multistage VQ
has been presented. In the proposed algorithm, the robust watermark is em-
bedded in the first stage using the robust watermarking method based on
index properties [20]. The semi-fragile watermark is embedded in the sec-
