Visual Cryptographic Scheme with High Image Quality

In order to avoid pixel expansion and contrast of the gathered secret image compromise, an easier visual cryptographic scheme, which was called visual cryptographic of interleaving with sub-block coding method, was presented. Instead of using m subpixels to represent one pixel, according to a key matrix, the secret image was divided into 2 shadow images, in which there were some background pixels useless. In shadow images, each pixel copied from the secret image maintained the exact value and position in the original secret image, therefore the secret image could be superposed, with interleaving, from the 2 shadow images exactly. Then sub-block coding method was adopted to convert each shadow image to numbers matrix, that is, every block met an unique number. After that, according to a secret key, these two number matrices were converted into a series of number. Last the series was encrypted to transport or do some other operations. This scheme was compared to the (k, n) Visual Secret Sharing scheme in Section 4 and it had been shown that there did not exist pixel expansion and contrast compromise in this new scheme, thus a better effect was presented.