Image Sharing with Steganography and Authentication - Visual Cryptography and Secret Image Sharing - page 450

TABLE 16.1
The cover-to-secret image size ratios of the
existing schemes and the proposed scheme.
Schemes Cover size / secret size

Lin-Tsai's scheme 4

Yang et al.'s scheme 4

Chang et al.'s scheme 2

Our scheme 2 / 3

TABLE 16.2
The detection ratios of different schemes.
Schemes

Detection ratios (DR)

Lin-Tsai's scheme 0%

Yang et al.'s scheme 52%

Chang et al.'s scheme 97%

Our scheme 79%

putational complexity or pixel expansion occurs with our scheme. Moreover,
in practice, the nearly 80% detection ratio is suciently effective.

16.6 Conclusions
In this chapter, we propose a novel secret image sharing and authentication
scheme in which the set of shadows and the reconstructed secret image are
generated through simple operations, and no computational complexity or
pixel expansion occur. The PSNR value of the reconstructed secret image is
larger than 30 dB, and the visual quality of the reconstructed secret gray-scale
image is acceptable.
Some research reported in the literature uses steganography as with
Shamir's secret sharing scheme [9,15,28]. However, with these approaches the
cover images must be many times larger than their secret images. For a se-
cret image of H W pixels, for earlier schemes (introduced in Section 16.2),
the cover image should be 2H 2W pixels or 2H W pixels in size. Such a
restriction requires more storage capacity in the cover image and consumes a
larger bandwidth during transmission. Experimental results confirm that each
shadow generated by our scheme is six times smaller than the secret image.
Moreover, the ratio of cover image size and secret image size is reduced to 2/3.
This is the primary advantage of our scheme over past work. To compare vi-
sual quality between cover images and their corresponding stego-images with
the earlier schemes and our proposed scheme, we used several images for our
experiments. The experimental results are shown in Figure 16.29. The PSNRs