Research On Relative Theories And Key Technologies Of Digital Watermarking For Three-Dimensional Mesh Models

With the rapid development and wide use of multimedia and network technologies, the copyright protection for multimedia has become the most urgent problem to be solved. Particularly, the copyright protection method for 3D models are far from mature as that of other kinds of media like digital image, audio, video and text. The traditional encryption technology protected the digital 3D models with great limitation. However, the new technology——digital watermarking technology can overcome these defects, which is a strong tool for multimedia content protection besides the encryption technology. Therefore, in this dissertation, the deep study on digital watermarking technologies for 3D models in the open network are made; three digital watermarking algorithms for 3D mesh models appropriate to different application background are proposed; and the system model of watermarking and mobile agent based digital right management, which implements the illegal copy protection and copyright tracking and diction for 3D models in the open network environment, is proposed. The main research work in this dissertation is as follows:1. A novel SVD(Singular Value Decomposition) based digital watermarking algorithm for 3D mesh models is proposed. The presented algorithm uses the length between the vertices on the mesh surface and the center of the model to constitute the vertices module matrix which embodies the global geometric characteristics of the whole model. So, the vertices module matrix can be taken as the plane parameters of the 3D models. On this basis, the SVD method can be used to embed one dimensional or two dimensional watermarks into the vertices module matrix. Then the 3D mesh models can be recovered from the watermarked vertices module matrix, and the watermark spreads all over the mesh model, which means it is difficult to remove the watermark from the model. Furthermore, because of the great stability of SVs, the algorithm is of good robustness. The experiment results presented in the dissertation indicate that the algorithm shows robustness, feasibility and has promising prospects. 2. For blind digital watermarking, on the basis of deep study on the technology of level of details, a novel blind digital watermarking based on progressive mesh is proposed. In the embedding process, the embedding location is selected by progressive mesh algorithm, which results in good concealing effects, robustness to noise attack and common geometric attacks. For the watermark information construction is relative to the vertex location and can be used as the key to detect the watermark. Only the one who owns the correct key can detect the watermark information, which ensures the security of the algorithm. When the original model is not attainable in the watermark detection process, this algorithm is appropriate. Furthermore, the algorithm shows great imperceptibility and robustness in the attacking experiment.3. A digital watermarking algorithm based on 3D model's range image is put forward. In order to attain great robustness, the area embodying apparent features of the 3D models is selected as the embedding area. The range images contain the important appearance features of 3D models; as a result, the range images are selected as the embedding area. Firstly, the principal component analysis is used to select the optimal view points of the 3D model. Then the range images in the direction of the optimal view points is attained and transformed into the Fourier domain. The watermark is embedded into the Fourier domain of the range images. Finally inverse Fourier transform is carried out and the watermarked 3D model is achieved. Because the range images are selected as the embedding area, the watermark is hardly to remove, if the attackers are unwilling to lose the visual value of the 3D model. The experimental results show that the algorithm is robust to attacks like simplification, rotation and scaling, brought by the rotation invariable feature of Fourier transform.4. In order to provide copyright protection to the 3D models in their whole life cycle under the open network environment, the model of WADRM(digital watermarking and mobile agent base digital right management system) is proposed. And an instance is illustrated to show the detail process of how WADRM provides copyright protection to the 3D models in their whole life cycle under the open network environment. Contents offering stage, verification stage of contents illegally copied, the process of creating and dispatching a mobile agent and the process of detecting the watermark based on mobile watermark are analyzed in detail. Comparing with the existing systems, when the illegal copy behaviors happened in the user's host, the hidden agent will automatically execute its code to terminate the malice behaviors arbitrarily so as to the purpose of the illegal copy protection. The WADRM doesn't need watermark detector or smartcard, facilitating the client usage; watermark detection is carried out by the mobile agent, which can effectively reduce the payload of the network; watermark detection is implemented in the remote host, the payload is shared in the remote hosts, avoiding the critical bottleneck; continuous connection is not necessary for mobile agent, and the detection result can be transmitted to the watermark agent center asynchronously; furthermore, the mobile watermark agent can adopt corresponding actions, when finding the illegal copying and unauthorized usage.