Enhanced visual secret sharing scheme via halftoning technique

The rapid development of networks such as internet, intranet, wireless communication etc., and multimedia techniques has emphasized on the need for copyright protection, authentication and identification and secret sharing of information. Visual cryptography is a secret sharing scheme where a secret binary image (SI) is encoded into n shares of random binary patterns. If the shares are xeroxed onto transparencies, the secret image can be visually decoded by superimposing a qualified subset of transparencies, but no secret information can be obtained from the superposition of a forbidden subset. The binary patterns of the shares, however, have no visual meaning and hinder the objectives of visual cryptography. Extended visual cryptography was proposed recently to construct meaningful binary images as n shares using hypergraph colorings, but the visual quality is poor. In this paper, a novel technique named visual secret sharing scheme using halftoning is proposed to achieve visual cryptography via halftoning. Based on the blue-noise dithering principles, the proposed method utilizes the void and cluster algorithm to encode a secret binary image into n halftone shares (images) carrying significant visual information. The simulation shows that the visual quality of the obtained halftone shares is observably better than that attained by any available visual cryptography method known to date.