A new construction algorithm of visual crytography for gray level images

In this paper a new construction algorithm of visual cryptography is presented. First, we extend SFCOD (space filling curve ordered dither - one of the techniques of halftoning) to transform a gray-level image into an image with fewer grayscale values. In addition, we extend the basic visual cryptography model to handle more than two grayscale values. Then the extended visual cryptography model can be applied to encode this image. This scheme satisfies the security and contrast conditions. It can reveal more details of original images in the decoded images than ordinary visual cryptography scheme.