In binary Region incrementing visual cryptography schemes (RIVCSs), the secrets of multiple secrecy regions can be gradually revealed by human visual system. A characteristic of the existing binary RIVCSs different from traditional binary Visual cryptography schemes (VCSs) is that, the contrasts for different revealed regions are different while traditional binary VCSs have same contrast. To keep the quality (contrast) of recovered image compatible with the traditional VCS, we use integer linear programming to design a binary (k, n)-RIVCS with same contrast for all secrecy regions in this paper. Experimental results demonstrate that our method is feasible and effective. The trade-off is that our scheme involves a larger pixel expansion.
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