Threshold Visual Cryptography Schemes with Specified Whiteness Levels of Reconstructed Pixels
Designs, Codes and Cryptography
Improved Schemes for Visual Cryptography
Designs, Codes and Cryptography
A General Formula of the (t, n)-Threshold Visual Secret Sharing Scheme
ASIACRYPT '02 Proceedings of the 8th International Conference on the Theory and Application of Cryptology and Information Security: Advances in Cryptology
Randomness in secret sharing and visual cryptography schemes
Theoretical Computer Science
Ideal contrast visual cryptography schemes with reversing
Information Processing Letters
Designs, Codes and Cryptography
Colored visual cryptography without color darkening
Theoretical Computer Science
On the security of a visual cryptography scheme for color images
Pattern Recognition
Dot-Size Variant Visual Cryptography
IWDW '09 Proceedings of the 8th International Workshop on Digital Watermarking
Halftone visual cryptography via error diffusion
IEEE Transactions on Information Forensics and Security
Ideal contrast visual cryptography schemes with reversing
Information Processing Letters
Optimal (k, n) visual cryptographic schemes for general k
Designs, Codes and Cryptography
Bounds for visual cryptography schemes
Discrete Applied Mathematics
A new definition of the contrast of visual cryptography scheme
Information Processing Letters
A new sharing secret algorithm in stego images with authentication
ICICS'09 Proceedings of the 7th international conference on Information, communications and signal processing
A comprehensive study of visual cryptography
Transactions on data hiding and multimedia security V
Improving the visual quality of size invariant visual cryptography scheme
Journal of Visual Communication and Image Representation
Colored visual cryptography without color darkening
SCN'04 Proceedings of the 4th international conference on Security in Communication Networks
Compatible ideal contrast visual cryptography schemes with reversing
ISC'05 Proceedings of the 8th international conference on Information Security
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
Image hatching for visual cryptography
ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP) - Special Issue on Multimedia Security
A new authentication based cheating prevention scheme in Naor-Shamir's visual cryptography
Journal of Visual Communication and Image Representation
Visual secret sharing with cheating prevention revisited
Digital Signal Processing
Sharing more information in gray visual cryptography scheme
Journal of Visual Communication and Image Representation
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A (k,n)-threshold visual cryptography scheme (VCS) is a method to encode a secret image SI into n shadow images called shares such that any k or more shares enable the "visual" recovery of the secret image. However, by inspecting less than k shares one cannot gain any information on the secret image. The "visual" recovery consists of copying the shares onto transparencies and then stacking them. Any k shares will reveal the secret image without any cryptographic computation. In this paper we analyze the contrast of the reconstructed image for a (k,n)-threshold VCS. We define a canonical form for a (k,n)-threshold VCS and provide a characterization of a (k,,n)-threshold VCS. We completely characterize a contrast optimal (n-1,n)-threshold VCS in canonical form. Moreover, for $n\geq 4$, we provide a contrast optimal (3,n)-threshold VCS in canonical form. We first describe a family of (3,n)-threshold VCS achieving various values of contrast and pixel expansion. Then we prove an upper bound on the contrast of any (3,n)-threshold VCS and show that a scheme in the described family has optimal contrast. Finally, for k=4,5 we present two schemes with contrast asymptotically equal to 1/64 and 1/256, respectively.