A construction of a visual secret sharing scheme for plural secret images and its basic properties

In this paper we discuss construction of the visual secret sharing scheme for plural secret images. We first consider generation of n shares for given two secret image SI₁ and SI₂. For i = 1, 2, while no information of SI_i is revealed from any less than n - 2 + i shares, SI_i is visually recovered by the superimposition of arbitrary n - 2 + i shares. We define a new class of basis matrices used for generation of the n shares and give a simple construction of such basis matrices. In addition, a fundamental bound on the contrasts of SI₁ and SI₂ is established. These results are extended to the case where we have more than two secret images.