Research On Watermarking 2D Vector Graphics

Daily life is becoming more and more colorful with the exchange of multimedia information. However,it's inevitable that problems such as illegal spread,malicious manipulation and piracy of multimedia are present. As a whole new mean to guard information security, digital watermarking technique has been an effective method for copyright protection and authentication on multimedia.At present, most research on digital watemarking focus on image watermarking,especially on robust watermark for copyright protection. As an important kind of multimedia information, graphic data also needs some kinds of method to protect its property and to authenticate its resource. These years watermarking on graphic data has been gained more attention.This dissertation first makes a simple analysis on the actuality of graphics digital watermaking, and then, based on the characteristics of two-dimensional vector graphics, makes a preliminary exploration on digital watermarking technology in the application of copyright protection and content authentication. The main work of the dissertation is summarized as follows:First, a new method of digital watermarking scalable vector graphics based on discrete fractional fourier transform is proposed. Different levels of the discrete fractional fourier transform are chosen for coordinates of control points and the watermark signal, respectively. Two different levels not only improve the security, but also provide a simple and feasible method to optimize the watermarking algorithm. Both high invisibility and robustness against common manipulations, such as geometrical transformations and local modifications, have been proved by experimental results.Second, in order to improve the watermark capacity and to minimize the distortion of the watermarked vector graphics, a novel technique using the combinational spatial and frequency domains is proposed. The embeddable points are selected according to their curvatures firstly, and then the binary watermark image is divided into two parts, respectively, for spatial and frequency insertion. Before detection, pre-processing is proposed to eliminate geometric distortions of test vector graphics. The algorithm not only improves the capacity of watermarks, but also enhances the security because of the dual watermarks. Robustness against common geometrical distortions and local modifications has been proved by experimental results.Finally, a semi-fragile digital watermarking algorithm based on 2D vector graphics is designed for tamper detection and localization. The construction of 8×8 matrix according to sorted vertices is transformed by DCT. Authentication watermark is generated by the relationship between the DCT coefficients, and then embedded in the middle frequency region of the coefficients."Super-cruve"is proposed to eliminate geometric distortions of test vector graphics before detecting. As the experiments shown, the algorithm can resist common geometrical distortions and has good capability of tamper localization.