Efficient constructions for progressive visual cryptography with meaningful shares

In a progressive visual cryptography scheme (PVCS), the clarity of recovered images can be enhanced by increasing the number of stacking shares. Noise-like shares are hard to identify, therefore, user-friendly progressive visual cryptography schemes (FPVCSs) generate meaningful shares. This paper proposes two encryption approaches to construct FPVCSs. One is a general OR-based FPVCS called (2, n)-FPVCS, and the other is an XOR-based FPVCS called (2, n)-XFPVCS. The common issues of the two models include: (1) systematic approaches, (2) avoiding the pixel-expansion, (3) providing adjustable visual quality of meaningful shares, and (4) eliminating residual traces of cover images. Moreover, the paper theoretically analyzes and carries out experiments to verify the visual qualities of the proposed two models. The experiment results indicate that the proposed approaches can accomplish these objectives simultaneously. In addition, (2,n)-FPVCS can adjust the threshold of trace-elimination by setting a parameter, which improves the flexibility of the proposed approach. As well as (2, n)-XFPVCS obtains a fully decrypted final recovered image. (C) 2019 Elsevier B.V. All rights reserved.