Abstract

Two common drawbacks of the visual cryptography scheme VCS are the large pixel expansion of each share image and the small contrast of the recovered secret image In this paper we propose a step construction to construct VCSOR and VCSXOR for general access structure by applying 2 2 -VCS recursively where a participant may receive multiple share images The proposed step construction generates VCSOR and VCSXOR which have optimal pixel expansion and contrast for each qualified set in the general access structure in most cases Our scheme applies a technique to simplify the access structure which can reduce the average pixel expansion APE in most cases compared with many of the results in the literature Finally we give some experimental results and comparisons to show the effectiveness of the proposed scheme