Random grid based color visual cryptography scheme for black and white secret images with general access structures

Abstract

To reduce the pixel expansion problem in color–black-and-white visual cryptography schemes (CBW-VCSs) and to provide flexible sharing strategy simultaneously, a random grid based CBW-VCS (RG-CBW-VCS) for general access structure (GAS) is proposed in this paper. First of all, the concept of random grid is extended to color pixel domain, and the XOR operation for color pixels is defined. By adopting this operation, a scheme for RG-CBW-VCS which implements the GAS is introduced. The proposed method is further extended to realize the generalized GAS (GGAS), where implementing complicated sharing strategy becomes available. Theoretical analysis on the proposed method are given to prove the security and contrast conditions, as well as the calculation of contrast. Experimental results are exhibited to show that optimal pixel expansion is achieved by the proposed method.