Research And Implementation Of 3D Model Watermarking Algorithms

Digital technology facilitates the distribution and storage of information, but brings out the problem of copyright protection. Digital watermarking is one effective way to solve the problem. Most of the current watermarking technology focuses on media types like still images, audio and video. In contrast, 3D watermarking has received less attention from researchers. But, more and more applications depend on CAD-based 3D data, accordingly, companies or copyright owners who present or sell their products on internet will face copyright protection problem. The straightforward demand is to prevent their 3D-based material from unauthorized use. As a new way for the protection of information copyright, digital watermarking possesses extensive application perspective in this area.First watermarking algorithm of 3D model is brought by Ohbuchi, and later some research had been done. But watermarking of 3D model technology is not mature because 3D model data is distinguishingly, especially 3D model can not be decomposed like image. We focus on research of 3D mesh watermarking based on the research state at home and abroad.We first introduce the background and meaning of 3D watermarking technology, and some basic concepts of digital watermarking. Then we expound the characteristic and classification of digital watermarking of 3D models. Then, we describe briefly the related work and research. According to the difference of watermark embedding approaches, three dimensional model watermarking can be divided into two kinds: Embed watermark in spatial domain and in frequency domain. According to this classification, we conclude and analyze the classic digital watermarking algorithms of 3D models, and describe their advantages and disadvantages.We design and implement a complete three-dimensional model watermarking system based on the characteristic of 3D model and function analysis of watermarking system. We introduce the organization and storage of 3D model data, and explain the implementation of each module in the frame briefly and clearly, generation and detection of watermark involved. The system integrates all of the common mesh attack operations, such as affine transformation, mesh simplification, random noise, cropping, smoothing etc, all of these algorithms are present. For some attack operations, preprocessing is needed sometimes before extract the watermark. The pre-processing including mesh registration and re-sampling, which can raise the exactness of watermark detection, is very important to the whole watermarking process. One typical algorithm of registration and re-sampling is introduced particularly.In this article, we propose a robust 3D mesh watermarking algorithm based on DCT intermediate frequency coefficients, consulted the research method of image watermarking. First, we take the "radius" of 3D model which represents the geometric characteristic of 3D model as a digital signal in spatial domain and transform it to signal in frequency domain using one-dimensional discrete cosine transform (DCT). Then we embed watermark into the intermediate frequency coefficients of signal in frequency domain, and at last transform it back to a digital signal in spatial domain using inverse DCT. Experiments show that this algorithm is both simple to implement and robust against common mesh attacks such as mesh simplification, cropping, random noise and so on with good transparency. The 3D model watermarking algorithm based on progressive mesh which proposed by E Praun is one of the most robust algorithm, but this scheme employed Hoppe's progressive mesh construct method, which is very complex and influences the efficiency of watermarking algorithm. We introduce the principle of progressive mesh detailedly, and give a simple and practical method for mesh collapse, which can be used in the watermarking process to improve the efficiency and guarantee the validity of progressive mesh construction. Experiments show that the watermarking algorithm based on the improved progressive mesh is robust too.In the end we summarize my works and some possible research directions of 3Dmodel watermarking in future.