The Theory And Technique Of Digital Watermarking Based On DCT And SVD

With the rapid growth of the Internet, it is very convenient for people to get access to multimedia data, which poses a challenge to copyright protection. Digital watermarking has been revealed to be an efficient technique to cope with the problem of copyright protection of multimedia data. This technology embeds the data into an unperceivable digital code, namely the watermark, carrying information about the copyright status of the work to be protected. There are two important issues that the watermarking need to be addressed. First, watermarking are required to keep the quality of the original data and imperceptibility. Second, watermarking should satisfy the requirement of the robustness and resist distortions due to common image manipulations.In this paper, the basic concepts and principles of digital watermarking are given first, and then some typical algorithms are introduced. A novel watermarking algorithm based on singular value decomposition (SVD) and discrete cosine transform (DCT) is proposed late, according to the principle and the advantages of the application of DCT and SVD. The algorithm includes the following two steps: (a) Apply the DCT to the whole image and map the DCT coefficients into four quadrants which represent frequency bands from the lowest to the highest; (b)apply the SVD to each quadrant, in which the singular values are modified by the singular values of the DCT-transformed watermark. The algorithm adopts the integrated technologies like DCT and SVD, and takes advantage of the imperceptibility property of DCT. While the property of SVD is stable, the secrecy and robustness of the watermark are enhanced, and then the aim of copyright protection is attained.By the end of this paper, experimental results generated by the algorithm are presented, and the algorithm is also compared with the pure SVD algorithm. The experimental results show that the algorithm referred in this theme can withstand a wide range of attacks. The digital watermarking embedded into images is proved to be transparent and robust.