Random grid visual cryptography scheme based on block encoding

The Visual Cryptography Scheme (VCS) allows secret images to be hidden in two or more shares. A solution to the problem of pixel expansion in conventional VCS was created: the Probability Scale Invariant VCS (P-SIVCS). However, a codebook needs to be written for P-SIVCS and VCS. Kafri’s Random Grid VCS (RG-VCS) did not require a codebook, however the revealed secret image was noisy. The random gird algorithms presented in this paper are both aesthetically pleasing and security relevant. This is also the first time that the first share of RG-VCS was chosen as a block instead of a uniform distribution, and it is also the first time that the concept of a multi-pixel was implemented in RG-VCS . In addition, compared to previous thresholding algorithms, the proposed algorithms have better performance in terms of contrast accuracy and visual quality according to theoretical analysis and experimental results.