Visual cryptography for general access structures
Information and Computation
A New Approach for Visual Cryptography
Designs, Codes and Cryptography
COCOON '08 Proceedings of the 14th annual international conference on Computing and Combinatorics
Bounds for visual cryptography schemes
Discrete Applied Mathematics
Journal of Combinatorial Optimization
Improvements of a two-in-one image secret sharing scheme based on gray mixing model
Journal of Visual Communication and Image Representation
On the equivalence of two definitions of visual cryptography scheme
ISPEC'12 Proceedings of the 8th international conference on Information Security Practice and Experience
On (k, n)*-visual cryptography scheme
Designs, Codes and Cryptography
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A visual cryptography scheme encodes a black and white secret image into n shadow images called shares which are distributed to the n participants. Such shares are such that only qualified subsets of participants can "visually" recover the secret image. Usually, the reconstructed image will be darker than the background of the image itself. In this paper we consider visual cryptography schemes satisfying the model introduced by Tzeng and Hu [A new approach for visual cryptography, Designs, Codes and Cryptography 27 (3) (2002) 207-227]. In such a model, the recovered secret image can be darker or lighter than the background. We prove a lower bound on the pixel expansion of the scheme and, for (2, n)-threshold visual cryptography schemes, we provide schemes achieving the bound. Our schemes improve on the ones proposed by Tzeng and Hu.