Efficient visual secret sharing scheme for color images

A kk-out-of-nn visual secret sharing scheme (VSSS) resolves the visual variant of the k-out-of-n secret sharing problem where only k or more out of n participants can reveal the secret by human visual system without any cryptographic computation. The best pixel expansion of the general k-out-of-n VSSS for c  -colored images was c×mc×m by Yang and Laih [New colored visual secret sharing schemes, Des Codes Cryptogr. 24 (2000) 325–335] where m is the pixel expansion of an existing binary k-out-of-n VSSS. Regarding the c-colored n-out-of-n   scheme, the best pixel expansion is (c-1)2n-1-c+2(c-1)2n-1-c+2 and c(c-1)2n-2-cc(c-1)2n-2-c when n is odd and even, respectively, by Blundo et al. [Improved schemes for visual cryptography, Des Codes Cryptogr. 24 (2001) 255–278]. In this paper, we propose a new c-colored k-out-of-n   VSSS by using a pixel expansion of ⌈log2c⌉×m that is more efficient than ever.