Visual cryptography encodes a secret binary image (SI) into parts of random binary patterns. If the actions are photocopied on transparencies, the secret image can be visually decoded by superimposing a qualified subset of transparencies, but secret information can not be obtained from the overlapping of a forbidden subset. Binary patterns of actions, however, have no visual meaning and hinder the goals of visual cryptography. Extended visual cryptography was recently proposed to construct meaningful binary images as actions using hypergraphic dyes, but the visual quality is poor. In this work, we propose a novel technique called visual half-tone cryptography to achieve visual cryptography through semitones.
Visual cryptography (VC), first proposed by Naor and Shamir in 1994, is a secret exchange method, which is based on black and white or binary images. Naor and Shamir proposed a cryptography platform, called visual cryptography (VC) or visual secret (VSS), which attempts to reveal the secret image through human perception of the visual system by stacking two or more parts. Visual cryptography is a unique concept of secret method of sharing, in this when actions are stacked, a hidden secret image is revealed.
Half-tone visual cryptography (HVC) extends the area of visual cryptography by adding digital halftone techniques. In particular, in visual secret sharing schemes, a secret image may be encoded in semitone shots by taking significant visual information. The secret image is embedded simultaneously in valued binary actions, whereas these actions are intermediate by diffusion of errors, the horsepower pattern of the semitone algorithms. Error diffusion has a low complexity and provides halftone quotas with good image quality. A reconstructed secret image, obtained by stacking the labeled parts together, does not suffer from cross-interference of the part's images.