具有优化对照度的灰度图像的可视分存方案

在可视分存方案（VCS）中，其解密过程通过人的视觉系统完成。对照度是VCS中重要的研究主题。现有复制设备提供了反色复制的基本功能，黑白图像的全黑反色方案（PBVCS）通过叠加一定数目的分存图像可以精确重构密图，从而为解决VCS重构图像质量问题提供了一种新的途径。给出了灰度图像的反色方案不能直接使用已有的全黑反色PBVCS来构造的原因和存在的问题，进而给出一般灰度图像的反色(k,n)-VCS，该方案的有效性被证明，使用我们的灰度反色VCS，对分存图执行有限次反色和叠加操作可正确重构密图。

Visual cryptography scheme for gray-scale images with optimal contrast

Visual cryptography scheme (VCS) is an encryption technique that utilizes human visual system in the recovering of the secret image and it does not require any complex calculation. Contrast has been a major issue of VCS schemes. Most copy machines have reversing function, in which can change a black image into a white one and vice versa. By means of the reversing operation, perfect black binary VCS with reversing can obtain ideal contrast. In this paper we conclude that we do not use existing VCS with reversing to construct an ideal contrast VCS for gray-scale images, then we show how to construct an ideal gray-scale VCS with reversing. In our scheme each participant is required to store a certain number of shares,and the number is same as that of binary VCS with reversing. Furthermore, the scheme guarantees that reconstructed image is correct since we perform certain runs operations.