The Research Of Digital Watermarking Scheme Based On Contourlet Transform

With the rapid development of computer network technology,everyone can distort the digital multimedia conveniently. So many people doubt the completeness and authenticity of the digital multimedia.Digital watermarking,an effective way of copyright protection, has already been paid attention by more and more pepole. It can prove the ownership of the author and can provide the evidence for the identification of the pirated digital media.There are two categories of watermarking processing methods: spatial domain methods and frequency domain methods. Spatial domain methods are relatively simple, but it can not resist the image attacks very perfectly. However,frequency domain methods can provide better robustness to the image attacks.The common digtal watermarking algorithm is based on DCT domain and DWT domain.With the development of the technology,contourlet transform is proposed by using pyramidad directional filter bank.In contrast with DWT, the main advantage of contourlet transform over other directional representations is that it allows different number of directions at each scale while achieving nearly critical sampling.In tis thesis, the watermarking algorithms based on DWT and contourlet transform are both studied detailedly and the robustness of the algorithm based on contourlet transform is better than that based on DWT.In order to achieve good effects both on robustness and invisibilitiy, a kind of robust watermarking algorithm combining dither quantization with singular value decomposition is discribed in the fourth chaper.The watermarking image is embedded into the maximum singular value of the decompotion host image by dither quantization and the watermarking image can be rebuilded without the original image.To improve the security of the algorithm,a new algorithm based on chaotic system is proposed. Firstly, the watermarking image is encrypted by logistic map.The host image is decomposed by contourlet transform,and the low frequency components in contourlet domain are separated in blocks.The maximum singular values of the blocks make up a new matrix. At last the encrypted watermarking image is embedded into the new matrix. According to the experiments of attacking test and watermarking effect,the results demonstrate that the watermarking system can achieve excellent performance both on visibility and robustness.The watermarking algorthm can resist several kinds of attacking operations such as image compress,noise interference and wave filter.