Extended Visual Cryptography Scheme for Multiple-Secrets Continuous-Tone Images

Abstract

Visual cryptography is a kind of cryptography that can be decoded directly by the human visual system. For instance, a secret image is obtained by simply stacking several transparencies. Extended visual cryptography is capable of introducing meaningful images on transparencies which can conceal the existence of “secret” in the transparencies. A scheme consisting of two techniques, parallel error diffusion and optimum tone mapping, can preserve image quality for encrypting continuous-tone images. It quickly encrypts images with no pixel expansion and achieves high contrast. This paper proposes a generalized scheme that can encrypt more than one secret images within transparencies. Different secrets can be reconstructed from different combinations of transparencies. Experimental results are also shown to examine the effectiveness of the new scheme.Keywordsextended visual cryptographyhalftoningerror diffusiontone mapping