An extended visual cryptography scheme for continuous-tone images

Abstract

Visual cryptography is a kind of cryptography that can be decoded directly by the human visual system when transparencies are stacked. Extended visual cryptography allows to print meaningful images on transparencies which can conceal the existence of "secret" in the transparencies. A lot of studies have tried to incorporate continous-tone images into extended visual cryptography. However, most of them suffer from deterioration of the resulting images. This paper proposes a new scheme for extended visual cryptography for continuous-tone images. It mainly consists of two techniques, namely parallel error diffusion and optimum tone mapping and can quickly encrypted images with no pixel expansion and high contrast. Some experimental results are shown to examine its effectiveness as well as limitation. © 2012 Springer-Verlag.