Visual Cryptography and Secret Image Sharing

8

Visual Cryptography and Contrast Bounds

Andreas Klein

Ghent University, Belgium

8.1 Introduction

8.2 Preliminaries

8.3 Approximate Inclusion Exclusion

8.4 Designs and Codes

8.5 Optimal 3-out-of-n Schemes

8.6 Asymptotic Optimal k-out-of-n Schemes

8.7 Contrast Trade-Offs for Extended Visual Cryptography Schemes

8.8 Enhancing the Contrast by Nonstandard Models

8.9 Conclusion

Bibliography

8.1 Introduction

To describe a visual cryptography scheme we encode the encryption of a pixel by Boolean matrices. The rows represent the slides and the columns represent the different subpixels.

For example, the encoding illustrated in Figure 8.1 is described by

M=(010100110110).

To describe the random decision, which must be made when encoding a pixel, ...