Image Sharing with Steganography and Authentication - Visual Cryptography and Secret Image Sharing - page 423

set to the Galois Field GF(2 8 ), that is, p = g(x) = x 8 + x 4 + x 3 + x 1 + x 0 .
This approach allows the acquisition of a secret image without distortion.
FIGURE 16.3
The cover blocks used in Yang et al.'s scheme.
FIGURE 16.4
The block of a stego-image in Yang et al.'s scheme.
In Yang et al's scheme, let the pixel I ij of the secret image be used to
produce the n shared pixels S ij , S ij ,...,S ij , to be embedded into the cover
blocks C ij ,C ij ,...,C ij , where each cover block is represented as C ij = fV ij ,
Y ij , Z ij , U ij g for 1 k n as shown in Figure 16.3. Pixel I ij of the secret
image is first embedded into the coecient c 0 to construct a polynomial as
shown in Equation 16.1. Next, the shared pixel S ij is computed by taking the
pixel value V ij of the corresponding cover image block C ij as the input x of
the polynomial shown in Equation 16.1. Let the binary representation of the
shared pixel S ij be (s 1 s 2 ...s 8 ). Hence, the shared pixel S ij is embedded into