Sunil Agrawal and Anshul Sharma, Panjab University, India

Visual cryptography encodes a secret binary image (SI) into 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. Halftone visual cryptography encodes a secret binary image into n halftone shares (images) carrying significant visual information. When secrecy is important factor rather than the quality of recovered image the shares must be of better visual quality. Different filters such as Floyd-Steinberg, Jarvis, Stuki, Burkes, Sierra, and Stevenson’s-Arce are used and their impact on visual quality of shares is seen. The simulation shows that error filters used in error diffusion lays a great impact on the visual quality of the shares.

Visual cryptography, error diffusion, halftone visual cryptography, secret sharing.