On the extension of XOR step construction for optimal contrast grey level visual cryptography

Step construction for visual cryptography which is applicable to both OR and XOR operation based reconstruction uses traditional (2, 2)-visual cryptographic scheme (VCS) recursively for generating shares. XOR step construction is the first deterministic general access structure scheme based on XOR reconstruction for binary images. The average pixel expansion of step construction is very less when compared to other general access structure schemes. Here in this paper, we extended XOR step construction to grey scale images and the comparisons with related work is shown. We also proposed a cheating immune VCS which is applicable to grey level images.