Visual cryptography for general access structures
Information and Computation
Extended capabilities for visual cryptography
Theoretical Computer Science
Improved Schemes for Visual Cryptography
Designs, Codes and Cryptography
Contrast Optimal Threshold Visual Cryptography Schemes
SIAM Journal on Discrete Mathematics
New Results on Visual Cryptography
CRYPTO '96 Proceedings of the 16th Annual International Cryptology Conference on Advances in Cryptology
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
Determining the Optimal Contrast for Secret Sharing Schemes in Visual Cryptography
Combinatorics, Probability and Computing
New visual secret sharing schemes using probabilistic method
Pattern Recognition Letters
Probabilistic Visual Cryptography Schemes
The Computer Journal
Image encryption by random grids
Pattern Recognition
Efficient visual secret sharing scheme for color images
Pattern Recognition
A multiple-level visual secret-sharing scheme without image size expansion
Information Sciences: an International Journal
A new definition of the contrast of visual cryptography scheme
Information Processing Letters
Journal of Visual Communication and Image Representation
Visual Cryptography and Secret Image Sharing (Digital Imaging and Computer Vision)
Visual Cryptography and Secret Image Sharing (Digital Imaging and Computer Vision)
Enhancing the perceived visual quality of a size invariant visual cryptography scheme
ICICS'12 Proceedings of the 14th international conference on Information and Communications Security
Improving the visual quality of random grid-based visual secret sharing
Signal Processing
Natural language letter based visual cryptography scheme
Journal of Visual Communication and Image Representation
Threshold visual secret sharing by random grids with improved contrast
Journal of Systems and Software
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In order to reduce the pixel expansion of visual cryptography scheme (VCS), many size invariant visual cryptography schemes (SIVCS's) were proposed. However, most of the known SIVCS's have bad visual quality and thin line problems, hence the known SIVCS's are only suitable to encrypt coarse secret images. In this paper, we notice that the variance of the darkness levels of the pixels also reflects the visual quality of the recovered secret image, as well as the average contrast. We verify, analytically and experimentally, the effectiveness of the variance to be a criterion for evaluating the visual quality of the recovered secret image. Furthermore, we propose two multi-pixel encryption size invariant visual cryptography schemes (ME-SIVCS's) which improve the visual quality of the recovered secret image by reducing the variance of the darkness levels. In addition, the proposed ME-SIVCS's can be used to encrypt fine secret images since they avoid some known thin line problems. Experimental results and comparisons are also given to show the effectiveness of the proposed ME-SIVCS's. Finally, we give suggestions on obtaining good visual quality for the recovered secret image.