| With the rapidly development of multimedia and network communication, the delivery of information becomes digitalized. However, digital media information is easily to be copied, processed, published and transmitted. Thus the problems of the safety and the reality of digital information transmission appear. Digital watermarking is a process of embedding watermark into digital products to prove the copyright, it provides a new valid solution to copyright protection. There is problem of copyright protection on vector map, the mature watermark algorithms of raster image are inconformity with the vector map data. Thus the study of vector map watermark has important theoretical and practical significance.The paper first introduces the basic knowledge of digital watermarking, including the concepts, theoretic framework and classification. Other relevant knowledge of digital watermark is introduced, such as Discrete Cosine Transform, Image Disorder and Human Visual System. After deeply analyzing the algorithm of vector map based on DCT at present, a DCT-based watermark algorithm of vector map is presented here.The watermark of vector map always be embedded into the middle frequency coefficients at present, and the intensity of watermark is fixed. The robustness of the watermark is bad. According to the character that the low frequency coefficients are more robust than the middle frequency coefficients, the watermark is embedded into the low frequency coefficients of the vector map, which can make the watermark more robust. At the same time, the algorithm is a blind one, which can extract the watermark without original vector map data. It presents the expression of the watermark intensity based on Watson visual model, which can make the watermark adaptively.The experimental results show that the proposed algorithm can ensure the accuracy of vector map data, and its robustness can resist the general attacks on vector map such as translation, rotation, scaling, cropping and noise. |
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