Research On Image Scrambling And Digital Watermarking Based On Singular Values Decomposition

The appearance of Internet and the widely use of computers open new avenues to the acquisition, the exchange and even the diffusion of the digital multimedia data. In the meantime, the problems of network safety come up. Anybody can stand to gain, reproduce and rework the original works by Internet, which seriously infringe on the copyright of the authors. Nowadays, the copyright protection of digital product, such practical problem, calls for immediate action. Under such circumstances, watermarking technology has emerged accordingly. It is the technique that proves the owner of copyright by using the watermark, which is embedded in the original work.Still image is used as the research object in this thesis, mainly research content is as follow.First, research and realization of algorithm of the image scrambling are discussed in Chapter 3. Algorithm of scrambling that is based on chaos is presented. Firstly, the author uses chaos sequence that produces by Logistic mapping to realize scrambling of an image by changing the positions of its pels points. Then the author uses Chebyshev chaotic sequence and Logistic chaotic sequence to realize the gray level scrambling by changing the pixels value. The simulation suggest that this algorithm has superior security, better scrambling result, and more efficient and less operation.Second, the paper introduces safety analysis of two kinds of watermark algorithm that is based on singular value decomposition (SVD). And this paper points out the potential safety hazard of such methods, and gives the method of estimating embedding strength or quantized value to realize the watermark attack. The experimental results show that the attack algorithm is effective and available in time.Third, the realization of digital watermarking algorithm based on quantization of singular values in wavelet domain is emphasized in Chapter 5. In this paper, an algorithm - a modified watermark algorithm, which is based on Block-SVD, is proposed on a basis of traditional watermark algorithm of SVD. This algorithm has two major differences between traditional one: first, watermark adopts grey image instead of binary image; second, on the premise of favorable robustness, this algorithm can stand against the attack as discussed in second part.