Colored visual cryptography scheme based on additive color mixing

摘要

A (t, n) visual cryptography scheme (VCS) encodes a secret image into n shadow images (shadows) distributed among n participants. When any qualified set of at least t participants stack their shadows, the secret image can be visually revealed. The first VCS proposed by Naor and Shamir was only designed for encrypting a black-and-white secret image; subsequently, some Colored VCSs (CVCSs) for sharing colored images were Proposed to enhance the applicability. In CVCSs, we usually use several color subpixels to represent a secret pixel where the number of subpixels is referred to as the pixel expansion. Generally, the CVCS requires a larger pixel expansion to produce more colors; however, this expansion will increase the shadow size. We therefore study the additive color mixing in a probabilistic way and propose a new CVCS whose pixel expansion is fixed and improves on the previous CVCSs, at the price of reducing the contrast quality to certain level. (C) 2008 Elsevier Ltd. All rights reserved.