| Summary: | 博士 === 國立中興大學 === 資訊科學與工程學系 === 105 === Multimedia is text, audio, two-dimensional and three-dimensional image, two-dimensional and three-dimensional video, and three-dimensional mesh collectively. Since the technology of computer has grown, there are more and more examples that people take an existed multimedia from Internet and claim it is their work after making a little alteration. Innovation and creativity are important for products. Therefore, copyright is an issue that has become importance and needs to be protected. There are some literature on the subject.
The algorithms were designed on blind fragile watermarking in this thesis. Utilize error correcting code and cryptography to enhance the attack verification ability. The objective is to protect the copyright of three-dimensional models. In this research, the meshes were used from a public database. These meshes refer to the virtual three-dimensional space in a computer by the point, line, surface, triangle, curve, and other geometric graphics and color design combination of virtual three-dimensional polygon modeling. The watermark can be used for detecting malicious modification and marking out the area from an attacked stego media. Therefore, the watermark should be embedded into all over the cover media as much as possible. However, embedding information will make some alterations on the media. It is tolerable if it cannot be noticed under human senses. The distortion ratio of each model is shown in experimental results.
This research can be divided into three parts. All of them are designed for protecting the polygonal meshes on computer. Experimental results show that they are efficient in reality applications.
(a)Extract data bits from a cover model and encrypted by error correcting code. Considered the output of the coding procedure is a watermark, which is embedded into the cover model itself. The advantage is that it can achieve lower time complexity than previous literature, control distortion ratio bellow 10-6, contain100% embedding capacity, and get efficient verification.
(b)Use cryptography, Feedback Mode, to encrypt a cover model. Extract a vertex as a plaintext, and consider the cyphertext as a watermark, which is embedded in the last significant bit (LSB) under decimal six or less after convert into binary. The advantage is that replace the LSBs can control the distortion rate. In the experiment results show that this algorithm can have high watermark embedding rate, high detect efficiency, low distortion rate and even more, higher security.
(c)A three-dimensional model has three coordinates (X,Y,Z). A spherical coordinate system (r,φ,θ) combine information with vertex, distance, and angle unit. Interaction between this three information can increase the tenacity of the algorithm. So that users can use a non-malicious way to moderately modify the appearance of a model, such as, scanning, zooming, and shifting, which is called affine transformation or geographic transformation. A geographic transformation is a mathematical operation that converts the coordinates of a point in one geographic coordinate system to the coordinates of the same point in another geographic coordinate system. A three-dimensional model is referred to virtual three-dimensional space in a computer by point, line, and surface. In a computer, a model is recorded by Cartesian coordinate system. Convert an input model from Cartesian coordinate system into spherical coordinate system in the very beginning. Then apply the first part and the second part encoding algorithm respectively by using a referenced vertex. The experiment results show that spherical coordinate system can resist affine attack efficient and still achieve high malicious attack detection rate.
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