Performance Evaluation of Visual Cryptography Schemes with Intensity Transformations for Gray-Scale Images

摘要

In a kind of visual cryptography, a secret image is hidden into other images. Then, we can reconstruct the secret image by using share images produced in secret image hiding scheme. In the case of two binary share images, the secret image is reconstructed by printing the two share images onto transparencies and stacking them together without any special electronic calculation. Myodo's method based on error diffusion can produce two high quality binary halftone share images from three input images, that is, two gray-scale images and a gray-scale secret image, and restore the gray-scale secret image hidden into their share images with high quality. The method changes intensities of each pixel in input images as a pre-processing in order to restore a high quality secret image. In this paper, we investigate intensity transformations to realize higher quality reconstructing of a secret image in myodo's method and we obtain that histogram equalization is effective to reconstruct a secret image with higher quality in term of visual effects.