Image encryption by random grids

A random grid in this paper is a transparency comprising a two-dimensional array of pixels that are either transparent or opaque determined in a totally random way. We design algorithms by using random grids to accomplish the encryption of the secret gray-level and color images in such a way that neither of the two encrypted shares alone leaks the information of the secret image, whereas the secret can be seen when these two shares are superimposed. The decryption process is done by our visual system and no computation is required. As compared to the approaches in visual cryptography, our algorithms do not need the basis matrices to encode the shares so that the problem of pixel expansion exists no more; that is, the sizes of the secret image and the encrypted shares are the same.