Watermarking And Anti-reconstruction Of 3D Models

With the rapid development of computing ability in graphics, more and more personal computers can process 3D models. The easy availability of 3D scanner and 3D software makes 3D models used diffusely in computer graphics, computer aided design and entertainment. Though information sharing and collaborative design benefit from Internet, copyright protection of 3D models becomes a serious problem because 3D models on Internet are easily copied and distributed without authentication. The reconstruction of 3D models from rendering data stream makes the problem more complicated. The results of the studies on watermarking and anti-reconstruction of 3D models are presented:Improved Two 3D Watermarking Algorithms: Nielson norm and the redundancies of triangle meshes are used in our first algorithm. Its performance is improved in robustness and visual quality. The original model is not required for watermarking detection and the visual quality of the model is not altered. The experimental results show that the algorithm is promising. The other algorithm we improved is a NURBS watermarking algorithm, which embeds watermark by inserting new knots. It is more robust than existing this kind of algorithms.Designed Three 3D Watermarking Algorithms: The first watermarking algorithm we designed is based on surface's principal directions. This method embeds the watermark information on 3D models by modifying the position of the vertices through moving vertices along their principal directions and it is robust against translation and rotation attacks. The second algorithm we designed is a local coordinate system-based 3D watermarking algorithm. A local coordinate system is created for each candidate vertex according to its one-ring vertices. The watermark information is embedded through modifying the coordinates of vertices in the local coordinate systems. And these positions keep unchanged when attacks such as rotation, translation and scaling are done to models, so this algorithm can resistant to these attacks. The original model is not required for watermark detection. The third algorithm we designed is a NURBS watermarking scheme based on iso-arc length sampling. The points sampled from NURBS are watermarked first, and then the watermarked NURBS surface can be constructed from watermarkedsample points. The later algorithm alters the NURBS shape slightly and it is more robust than the former one. The original NURBS surface does not required to detect watermark for both algorithms.Designed an Anti-3D Model Reconstruction Solution: Most 3D applications render 3D models through invoking OpenGL or DirectX 3D runtime libraries. The APIs of both libraries have their specification for the data to be transferred and rendered. Precise 3D models can be reconstructed by parsing the data streams transferred to OpenGL or DirectX 3D. To avoid reconstruction, the data of 3D models is encrypted before being transferred and rendered, then the 3D APIs are called with encrypted data, and the decryption is done in vertex shader after the data has passed through the 3D APIs.