Polynomial-Based Image Sharing - Visual Cryptography and Secret Image Sharing - page 411

and 43.44, respectively. The target secret image, shown in Figure 15.6 (a) could
be revealed when the (2; 4)-threshold was applied, via the four stego-images
shown in Figures 15.6 (b 0 ){(e 0 ). The experiments to embed Figure 15.6 (a) and
the resulting PSNR are summarized in Table 1. In addition, the revelation
of the target secret image was the same as Figure 15.6(a) when the (2; 4)-
threshold was applied in the stego-images, as shown in Figure 15.6(b 0 ){(e 0 )
and oered in Wang et al.'s scheme. It can be seen that signicantly improved
delity was achieved in Wang et al.'s scheme with the higher PSNRs, when
compared to other studies [4, 12].
Now considering another case, the (4; 6)-threshold scheme is used to embed
two target secret images, as shown in Figure 15.7 (a) and (b). The six cover
images are shown in Figure 15.7 (c) (h). The size of each target secret
image is

1

4 of each cover image. After SEDA, the corresponding six stego-
images can be seen in Figure 15.7 (c 0 ){(h 0 ). The PSNR measurements for the
discriminations between the six cover images in Figure 15.7 (c){(h) and stego-
images in Figure 15.7 (c 0 ){(h 0 ) were evaluated as 43.39, 43.43, 43.42, 43.39,
42.95 and 43.05, respectively, as shown in Table 2. Accordingly, the quality of
the stego-image was visually acceptable, when compared to the corresponding
cover images upon the high PSNRs. On the other hand, the target secret
images, shown in Figures 15.7 (a) and (b) could also be exactly revealed when
the (4; 6)-threshold was applied, via the six stego-images shown in Figures
15.7 (c 0 ){(h 0 ).
As seen below, colored benchmark images are further considered to the
embedding system via SEDA. The target secret image is shown in Figure 15.8
(a). These show the experimental results, using full color cover images. The
PSNR measurements were evaluated as 43.39, 43.12, 43.41, and 43.40, respec-
tively, for the discriminations between the cover and stego-images, shown in
Figures 15.8 (b){(e) and (b 0 ){(e 0 ). The comparisons, between the PSNR mea-
surements in Wang et al.'s and some other studies are presented in Table 15.3.
The (2; 4)-threshold scheme was applied, in this case, among the stego-images
shown in Figures 15.8 (b 0 ){(e 0 ). The target secret image can be seen to be
totally revealed, and identical to the original, shown in Figure 15.8(a).

TABLE 15.1
PSNR comparisons for past schemes and our scheme.
Bridge Buttery Toys Airplane

Lin-Tsai-scheme (PSNR) 39.11 39.13 39.23 39.16

Yang et al. scheme (PSNR) 41.61 41.46 41.44 41.69

Wang et al. scheme (PSNR) 43.42 43.43 43.41 43.44

15.5.2 Evaluating Authentication
In this section, the detection ability of the Lin-Tsai scheme, Yang et al.'s
scheme and Wang et al.'s are discussed. These are then compared, as shown
in Figures 15.9{ 15.11.