Research On Digital Image Watermarking

The digital information revolution has brought about many profound changes inpast decade, and generated many new challenges and opportunities in our society andour lives. For example, how to protect copyright of digital information? Digitalwatermarking may be a good way to resolve the issue, and thus has become a hotresearch topic. This dissertation is mainly concerning digital image watermarkingproblems. In Chapter 2, a detailed survey on digital image watermarking is presented. InChapter 3, an optimal scheme is proposed to use Human Visual System model tocompute masking function. It will be used to control the strength of watermark signalfor optimal embedding. In Chapter 4, we propose a novel watermarking scheme based on lattice vectorquantization. Some important transform coefficients of the original image are firstlymapped into the nearest neighboring lattice points by using lattice vector quantizer,then watermark signal is added to the lattice points. In the detection phase, the samelattice vector quantizer must be adopted to get lattice points as well as watermarksignal. If the watermarked image is attacked severely, the detected watermark signalwould be corrupted. Based on transmit diversity technique, we consider continuous tone color imageas three independent slowly fading channels in Chapter 5. Modulated and interleavedby different pseudo random sequences, the same watermark signal in different form isput into three different color channels simultaneously. Two watermark extractionmethods based on transmit diversity are proposed to improve detection accuracy. In Chapter 6, attentions are paid to the applications of digital imagewatermarking. We propose a new invisible watermarking technique for imageauthentication application. It combines image feature and public key cryptography.Theoretical analysis and experimental results demonstrate its good performance. Inaddition, we also propose a semi-fragile watermarking scheme based on lattice vector iiquantization. In a word, digital image watermarking, an immature technique, is very importantto digital copyright protection, authentication and secret communication. As we know,there are still many interesting and open problems to be resolved.