Abstract
With the progress in digital storage and transmission technology, digital data has become very popular, and the copyright issue is very important. Digital watermark embeds copyright information such as author declaration, version control, or CGMS (Copyright Generation Management System) into source data. It is a potential solution for copyright protection.The chief defect of watermarking is to decrease image quality. This is unacceptable especially for high quality digital source such as DVDs. It is hard to embed watermark without any defect of image quality when high robustness is required. Many researches address on HSV, affecting image data in a just-notified-defect sense. However, HSV is experimental and hard to find an objective model. Although image quality is important, there are still many applications that require strong robustness despite the image defect. Indeed, it is a trade-off between watermark robustness and image quality. In this thesis, we develop a complete scheme that takes watermark robustness or image quality as the constrained parameter and optimizes the other. The proposed watermarking scheme is based on wavelet transform. We embed copyright information into the best coefficient location in a rate-distortion sense. With the proposed algorithm, we can optimize the watermark robustness under the constrained image quality. On the other hand, we can optimize image quality under the watermark robustness constraint. Moreover, we encode the embedded information with error-correction coding. This adaptive and error-correction watermarking scheme is very suitable for CGMS in DVD II.The proposed algorithm takes advantages on three key concepts: (1) The hierarchical subband characteristics of wavelet transform (2) Rate-distortion theory in solving a constrained problem (3) Error-correction code for embedded information. Experimental result shows that our scheme will take good balance in watermark robustness with image quality.