A study on the Digital Watermarking and Copyright Protection Method for 3D Geometric Models

本研究的目的是为CAD、CAM、CAE和CG等领域的三维几何模型开发新的数字水印方法。水印是一种将不可见的水印秘密地嵌入到原始数据中的版权保护方法。该方法基于小波变换和三维几何模型的多分辨率表示，首次利用商用三维CAD系统设计了大规模的多边形、实体和曲面模型。通过在模型上嵌入水印、模型的坐标变换和修改、水印提取等一系列操作，对水印的鲁棒性、可嵌入水印的容量以及水印嵌入引起的几何误差进行了定量评价。得到了以下结果：（1）嵌入的水印在仿射变换下保持完整。(2)该方法能使模型的几何误差控制在规定的公差范围内。(3)嵌入的水印对噪声叠加、顶点修改等攻击具有较好的鲁棒性。(4)嵌入的水印对模型的裁剪操作鲁棒性较差，并对该水印算法进行了改进，使其适用于数字地图等二维矢量数据的水印嵌入。实验结果表明，该算法能够保持数据的视觉质量，水印容量足够大，能够存储版权数据，并且对顶点坐标上叠加的噪声具有很强的鲁棒性。算法的修改将是必要的，使得嵌入的水印对于2-D或3-D的裁剪操作变得更鲁棒。三维几何模型。

The purpose of this research is to develop the new digital watermarking methods for 3D geometric models in the area of CAD, CAM, CAE and CG.Watermarking is one of the copyright protection methods where an invisible watermark is secretly embedded into the original data. The proposed watermarking method is based on wavelet transform and multi-resolution representation of the 3D geometric models.In this research, large-scale polygon, solid and surface models were firstly designed using commercial 3-D CAD systems. Then the series of operations consisting watermark embedding on these models, coordinate transformation and modification of models, and watermark extraction were executed in order to evaluate the performance of proposed watermarking method.The robustness of the watermark for external attacks, capacity of embeddable watermark and the geometric error caused by watermark embedding were evaluated quantitatively. The following results were obtained ;(1) The embedded watermarks were completely kept under the affine transformation.(2) The geometric error of the models caused by the embedding could be easily kept within the specified tolerances.(3) The embedded watermarks were robust to the several attacks such as noise superposition and vertex modification on the models.(4) The embedded watermarks were not robust to the cropping operation for the models.Furthermore, the developed watermarking method was improved so as to be applied to the watermarking for 2D vector data such as digital map. As a result of the experiment, it was verified that the visual quality of the data could be kept, the capacity of the watermark was large enough to store the copyright data, and the watermark was very robust to the noise superposition on the vertex coordinates.In the future, the modification of the algorithm will be necessary so that the embedded watermark becomes more robust to the cropping operation for the 2-D or 3-D geometric models.