Halftone visual cryptography via direct binary search

This paper considers the problem of encoding a secret binary image SI into n shares of meaningful halftone images within the scheme of visual cryptography (VC). Secret pixels encoded into shares introduce noise to the halftone images. We extend our previous work on halftone visual cryptography [1] and propose a new method that can encode the secret pixels into the shares via the direct binary search (DBS) halftoning method. The perceptual errors between the halftone shares and the continuous-tone images are minimized with respect to a human visual system (HVS) model [2]. The secret image can be clearly decoded without showing any interference with the share images. The security of our method is guaranteed by the properties of VC. Simulation results show that our proposed method can improve significantly the halftone image quality for the encoded shares compared with previous algorithms.