Watermarking For 3D Models

With the development of computer graphics, games and virtual reality etc. The 3D objects are applied widely. And then the danger of illegal owned, copying, changing, transmitting copyrighted data without authorization is generated. The owners'copyrights are treated roughly. As a useful information security technique, the 3D object watermarking is becoming one of the research interest in the field of watermarking.Current watermarking technology focuses on media types like still images, audio and video streams, digital documents and so on. In contrast, the problem of watermarking 3D objects has received less attentions from researchers. But following the consciousness of copyright protection, the community or the individuals are paying more attention to it. So the 3D objects watermarking will possess extensive application perspective in this area.In this article, we have analyzed the technologies of 3D objects watermarking based on the watermarking method of still images, audio and video streams. And presented two methods respectively in the spatial domain and transform domain.In spatial domain methods, we analyzed the data structure of 3D objects and affine invariant space. First, a transformation of the model to an affine invariant space is finished prior to watermark embedding. Using the relationship of 3D objects'original data ,embedding the watermarking in the radius of spherical coordinates. Considering the visual masking, we used median and average method to embed the watermarking, and experiments show the availability of the result.In transform methods, we researched the DCT(Discrete Cosine Transform) and DWT(Discrete Wavelet Transform)deeply. Contrasted the spatial domain methods, the transform domain methods have better robust result. But based on the special data structure of 3D objects, it is more difficult to find the transformed data than the still images. In order to using transform domain method, we transform the objects to an affine invariant space as the spatial domain method,and it is useful to the geometry robust in some degree. then we change the 3D object to the spherical coordinates, choosing the embedding positions by the angle of spherical coordinates, and embed the watermarks in the radius of spherical coordinates. Because the slow speed and complicated of high dimension DCT and DWT, we produce a 1D signal from the radius of spherical coordinates, and perform a transform on it, then embed the watermark by changing the frequency coefficients. In experiments analysis, we show our result through images and tables, and compared the spatial method with the transform domain method.