New extended visual cryptography schemes with clearer shadow images

摘要

Visual cryptography scheme (VCS) encodes a visual information (pictures, text, etc.) into several noise-like shadow images. In VCS, each shadow image can be made on a transparency. By stacking transparencies and stack them on an overhead projector, we can visually decode the secret through human visual system without the assistance of any hardware or computation. However, noise-like shadows of VCS were suspected to censors and difficult for identification and management. Therefore, the extended VCS (EVCS) with meaningful shadow images had been proposed to address this problem of suspicion. In this paper, we employ a digital halftoning technology to propose a new EVCS whose shadow images are clearer in comparing with existing EVCSs.