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.

of participants have no information about the secret image. Pixel expansion, which represents the number of subpixels in the encoding of the secret image, should be as small as possible. Optimal schemes are those that have the minimum pixel expansion. In this paper we study the pixel expansion of hypergraph

Abstract: This paper explains the 2 out of 2 visual cryptography schemes based on pixel expansion m=2 in detail. Visual cryptography enables the secure transmission of images in open and insecure media. The scheme explained in this paper is based on k out of k visual cryptography scheme. To prevent

Abstract—Since the introduction of threshold visual cryptography by Naor and Shamir, there have been many other schemes proposed; some of them support color images with a limited number of color levels while a few others achieve the property of no pixel expansion. However, it is unknown

case, loss of resolution, contrast, and image size expansion are challenging problems that the researchers are facing. In this paper, we propose a method for processing halftone images that improves the quality of the recovered images and also avoids pixel expansion. The resulting scheme maintains

Visual cryptography is a secret sharing scheme which uses images distributed as shares such that, when the shares are superimposed, a hidden secret image is revealed. In extended visual cryptography, the share images are constructed to contain meaningful cover images, thereby providing opportunities for integrating visual cryptography and biometric security techniques. In this paper, we propose a method for processing halftone images that improves the quality of the share images and the recovered secret image in an extended visual cryptography scheme for which the size of the share images and the recovered image is the same as for the original halftone secret image. The resulting scheme maintains the perfect security of the original extended visual cryptography approach. Index Terms — cryptography, image processing, visual cryptography, secret sharing Table 1. Illustration of a (2, 2) VC Scheme with 4 Subpixels 1.

scheme achieves better contrast and reduces the noise in the reconstructed secret image without adding any computational complexity. In this technique the number of white pixels in the reconstructed secret image can be

Pixel Expansion has been one of the problems of Visual Cryp-tography that is yet to be properly addressed. Existing meth-ods to deal with this problem either have security vulnerabil-ities and/or produce results of poor quality. In this paper we propose a grouping based approach to encoding shares

no information regarding the secret image. In this paper a maximal independent sets of the graph G was applied to propose a lower bound on the pixel expansion of visual cryptography schemes with graph access structure (G). In addition a lower bound on the pixel expansion of basis matrices C5 and Peterson graph

the energy. The second move we consider is an α-expansion: for a label α, this move assigns an arbitrary set of pixels the label α. Our second