| Digital watermarking is a bran-new technology in the decadal years, that is, a sign signal (watermark) is embedded in original information (such as image, audio, and video) to realize copyright protect. In this thesis, the emphasis is laid on image watermarking technology, the focus of research in communication domain.In the first chapter, a general study and summarize of digital watermarking is given, including the background and significance of this project, the conception of watermarking, the characteristic and sort of watermarking, the applications domain and system figure of watermarking. In the second chapter, the stress is laid on analyzing predominance of watermarking in frequency domain, the optimal position where watermark is embedded and a number of classical algorithms in frequency domain. In the third chapter, all kinds of attacks against watermarking are summarized by attack types, including simple attacks, synchronization attacks, removal attacks, ambiguity attacks. Respective countermeasures are brought forward at the same time. Ultimately the foreground and the research direction of watermarking attacks in future are indicated.In the forth chapter, an algorithm of digital image watermark based on multi-resolution wavelet analysis is introduced, that is, a zero-one sequence is embedded in gray image. All pixels' mean value of original image is used, so the algorithm can be widely used. Experiment results show that the algorithm keeps the quality of the image (image with watermark is almost the same with original image from to human visual system) as well as robustness against common image processing operations (such as noise barrier, filtering, all kinds of compression). Based on the forth chapter, in the fifth chapter, an algorithm that gray image as watermark is embedded in original color-image is introduced. This algorithm think over both unobtrusiveness and robustness, and the size of image is unlimited. So it has strongly practical significance. |
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