Sharing a secret gray image in multiple images

In a traditional visual cryptography scheme, a shared secret image can be revealed with no cryptographic computations. Unfortunately, the revealed secret image of a conventional visual cryptography scheme is almost black and white. Colored visual cryptography schemes based on modified visual cryptography were recently proposed. By means of a few additional computations, users can hide a colored secret image. However, the implementation complexity in these schemes depends on the number of colors appearing in the secret image. In other words, when the secret image contains a large number of colors, these schemes will become impractical. In this paper, we propose a new secret color image sharing scheme based on modified visual cryptography. This scheme provides a more efficient way of hiding a gray image (256 colors) in different shares. Furthermore, the size of the shares is fixed; it does not vary when the number of colors appearing in the secret image differs.