Hiding secret data adaptively in vector quantisation index tables

Digital data hiding applications have been developed mainly with a view for sending secret information safely through the Internet or other computer networks. Most of the existing vector quantisation (VQ)-based data hiding methods, however, are capable of embedding only a limited quantity of secret data into the medium, usually a secret bit in every block at most. To improve the embedding capacity without seriously sacrificing qualities of carrier media, an adaptive VQ-based data hiding scheme based on a codeword clustering technique is presented. After the adaptive clustering process, the proposed scheme embeds secret data into the VQ-index table by performing codeword-order-cycle permutation. With the help of the cycle technique, more options can be offered for proper codeword substitution, which adds more flexibility to the whole data hiding scheme and therefore improves the quality of the embedded image. As the experimental results demonstrate, the proposed scheme is capable of providing better image quality and embedding capacity than the currently existing VQ-based hiding schemes. In fact, the stego-image quality is so good that it is visually indistinguishable from the VQ-compressed image.