Visual Cryptography Schemes with Reversing
The Visual cryptography scheme (VCS) is a perfect secure method that encrypts a secret image by breaking it into shadow images. A distinctive property of VCS is that one can visually, without computation, decode the secret by superimposing shadow images. However, much of the contrast of the reconstructed image is lost. A different kind of VCS has been recently proposed by Viet and Kurosawa, called VCS with reversing, allowing participants to perform a reversing operation (reverse black and white) on shadow images. Two drawbacks of the Viet-Kurosawa VCS are: (1) one can only reconstruct an almost ideal contrast image but not an ideal contrast image and (2) the Viet-Kurosawa VCS is constructed just from a perfect black VCS. This paper shows a real perfect contrast VCS such that the black and white pixels are perfectly reconstructed within finite runs, no matter what VCS (perfect black or non-perfect black) is used.
visual cryptography scheme shadow image ideal contrast