(k, N) Color Research And Application Of Visual Points Deposit Scheme

As a kind of cryptography, Visual Cryptography encodes a secret image into several images, from which we can’t get any information. However, its decryption is completed directly by human’s visual system without any complicated mathematical calculation. So Visual Cryptography is a very good plan when we can’t use the computer decryption. The initial Visual Cryptography can only be applied to the binary image, accompanied by two big problems of pixel expansion and contrast loss. When Visual Cryptography is applied to grayscale images and color ones, pixel expansion and contrast loss problems have become worse and worse that they have a direct influence on the application of visual cryptography in real life. In this paper, we propose a new visual cryptographic method for chromatic images with no pixel expansion and less contrast loss. Here, we use the idea of multi-point encryption, taking m continuous points as encryption sequence each time to commit encryption. This could make sure that there must be b encryption sequences using fundamental matrix with blacks points and the other (m-b) ones are encoded with fundamental matrix with white points, in m encryption sequences with b black points each. Moreover, it ensures a regular transformation in the stacked image with black and white. We further analyze the values of m on the basis that pixel does not expand, and find that the contrast ratio loss of encryption result is the least when m equals2.For chromatic images, this paper uses the principle of color model to decompose an initial chromatic image into three monochromatic images of cyan, magenta, and yellow. Using halftone technology, we transform the three monochromatic images into three binary images, which are then encoded and decomposed into n share images separately with the multi-point encryption method. Finally, we overlap the i-th share image of each binary image into the i-th chromatic share image, and these n sheets will be assigned to n different participants. The experimental results prove that the method in this paper completely overcomes pixel expansion problem and share images have sufficient security. In visual effect aspect, the contrast ratio loss of encryption results is very small and the restoring images are also very clear, when the value of m is2.