Research On Adaptive Vector Map Watermarking Algorithm Based On DFT

The digitalization of multimedia data provides much convenience for the storage and extraction of multimedia information. The efficiency and veracity of information expression has got greatly improvement recently. However, the problem of pirate is coming correspondingly. How to ensure the security of this information becomes a hotspot in current research fields. As an important branch of information hiding technologies, watermark has played a main role in the copyright protection. In order to resist the pirating and juggling for digital production, watermark technology could ensure the property and integrality by embedding hidden information into the original data. The application of digital watermark for the copyright protection of digital maps is mainly discussed in the thesis.Background, basal conception, and applications about watermark are introduced. Sorts and data structure of vector map are also analyzed. Some key techniques about watermark of vector map such as Discrete Fourier Transformation, pretreatment of watermarking, MQUAD algorithm are introduced in detail.Through studying existing watermark techniques, which have greater accuracy deviation and less robust after watermark embedded, a new DFT-based adaptive vector map watermarking algorithm is presented for authenticating copyright and tracking peddler. A scrambled binary image is used as watermark in this algorithm and embedded in point layer of the map. First of all, the map is divided into blocks according to the MQUAD algorithm. The intensity of watermark is modulated adaptively according to the density of vertices and the DFT amplitude of middle frequency coefficients in each block. Then the scrambled binary image watermark sequence is embedded in DFT middle frequency coefficients. The experimental results show that the proposed algorithm can ensure the accuracy and resist attacks, such as zooming, rotation, clipping, having better robustness.