Watermarking Algorithms On NURBS Surface With 3D-DCT

More and more 3D models appear on the Internet with the development of the computer and Internet technology. Especially the NURBS models, because of its mini volume and powerful modeling capacity, gain more and more people's favor. But with the widely use of the NURBS model, intentional or unintentional act of tort often occurs. In this condition copyright protection becomes very important. My research on NURBS watermarking technology starts under this condition. Watermarking technology as one of valid format of copyright protection is wildly researched in recent years. My work can be summarized into the following parts base on the research of the current main NURBS surface watermarking algorithms.Firstly one watermarking algorithm on NURBS surface with 3D-DCT was proposed. This algorithm is one spread spectrum robust watermarking algorithm. In the algorithm watermarking information is embedded into the three Dimension Discrete Cosine Transform (3D-DCT) coefficients which make the algorithm have the ability to resist the attack of affine transformation, knot insertion and some other attacks, and at the same time 3D-DCT technology makes this algorithm have the better power syntaxes nature. Watermarking information is distributed in three dimensions which make the algorithm have better resisting noise ability.Another work of my research is proposing an algorithm to adjust the local figure in the process of NURBS surface constructing. The watermarking algorithm in this thesis demands reconstructing NURBS surface after watermarking information is embedded into the sampling points. According to the sampling rule in the watermarking algorithm, the sampling points in the process of extracting watermarking information should approach the sampling points before the NURBS surface reconstructing, but common NURBS surface constructing algorithm can not finish this task perfectly, especially to the NURBS surface with complex surface. The local figure adjust algorithm adjust the NURBS surface local figure according the sampling rule, which makes the NURBS surface satisfy the request above as possible in order to improve the validity of the watermarking algorithm, in some degree this algorithm also improve the fidelity of the watermarking algorithm.