Multi-threshold image secret sharing scheme

From the point of view of information hiding, traditional visual cryptography scheme (VCS) is not an efficient method. It can only share a small sized secret image due to the large pixel expansion. A (t, k, n) multi-threshold image secret sharing scheme is proposed to increase the amount of hidden information. A grayscale secret image is hidden in a VCS to guide the choice of share matrices. In the first phase of the reconstruction process, any t participants can stack their shadow images to decode a vague secret image by human visual system. In the second phase, any k participants can extract additional information hidden in their shadow images, and reveal a precise grayscale secret image by computation. Compared with the traditional VCS, the proposed scheme can hide more information of the grayscale secret image, and has smaller size expansion without deteriorating the visual quality of the revealed image of VCS.