Generalized random grids-based threshold visual cryptography with meaningful shares

• A generalized RG-based VC with meaningful shares is proposed.
• The proposed VCS is for case (k, n) with no pixel expansion and no codebook design.
• The proposed VCS has many features that previous VCS fails to have.

The meaningful share in visual cryptography (VC) is a desired feature because it can increase the efficiency of management and decrease the suspicion of secret image encryptions. Although the traditional user-friendly random grid (RG)-based VC can produce meaningful shares, with the advantages of no pixel expansion and no need for codebook design, current user-friendly RG-based VCs fail to support the general (k,n)(k,n) threshold and the complementary shares might be required. In this paper, a generalized RG-based VC with meaningful shares is proposed. Besides inheriting the good features of no pixel expansion and no codebook design, the proposed scheme can support (k,n)(k,n) threshold and provide adaptive visual quality, at the cost of slightly decreasing visual quality of shared images. Our main contribution is to propose a meaningful VC for case (k,n)(k,n) with no pixel expansion and codebook design. To the best of our knowledge, the proposed scheme is the first method with all of these good features. Both the theoretical analysis and simulation results demonstrate the effectiveness and security of the proposed scheme.