An Optimized Halftone Visual Cryptography Scheme Using Error Diffusion

Halftone Visual Cryptography (HVC) is an encryption technique that encodes the secret image into halftone images in order to produce secure meaningful shares. Many methods have been proposed for developing HVC to protect the security of the images. Yet, these methods still have some problems such as poor visual quality of shares, large pixel expansion, interference of secret image on shared images, and interference shared images on retrieved image. To solve such problems, an optimized HVC scheme (OHVCS) using Error Diffusion (ED) is proposed in this paper. The proposed scheme eliminates the explicit requirement of codebook and reduces the random patterns of the shared images, as it encodes only the black pixels of the secret image, taking into account that the pixel expansion is the smallest size to be used. Moreover, it performs the basic concept of Visual Cryptography (VC); therefore, the security of the construction scheme is assured. The experimental results, performance evaluation through statistical analysis, and comparison with some existing schemes in various aspects of HVC show the effectiveness of the proposed scheme.