一种无损恢复的多级别的可视密码方案*

针对传统可视密码方案存在像素扩展且只能恢复一幅秘密图像的问题，提出无像素扩展的多秘密可视密码方案。基于随机栅格理论和异或运算对多个级别的秘密图像进行分存，对各个级别的分存图像进行异或即可依次恢复所有级别的秘密图像。可以实现二值秘密图像的无损恢复，并可扩展到灰度图像和彩色图像。图像传输引入纠错编码机制，提高方案的可靠性。实验结果表明分存图像没有像素扩展，恢复图像与原秘密图像相比无失真且能满足安全性要求。

A multi-level visual cryptography scheme with lossless recovery

Traditional visual cryptography schemes presented pixel expansion and could only share one secret image. This paper proposed a multi-level visual cryptography scheme without pixel expansion. The scheme processed multiple secret images based on random grids and XOR operation. Using XOR operation on each level could recovery all secrets respectively. It could realize lossless recovery of binary secret image, and could be extended to the gray image and color image. Image transfer process introduced error correction encoding mechanism to improve the reliability of the program. Simulation experiments demonstrate that the share images have no pixel expansion and the recovery images are the same as the original images. The analysis shows the scheme meets the security requirement.