電腦圖學領域的相關研究發展愈來愈蓬勃，除了電腦圖學本身的研究議題，也開始有許多跟其它領域結合的研究題目。以三維模型資料為掩護媒體的資訊偽裝便是電腦圖學跟資訊安全相結合的一個跨領域題目。資訊偽裝又稱資料隱藏，跟浮水印一樣都是資訊安全中非常重要的資訊隱藏範圍的研究議題。跟以認證及授權為目的的浮水印不同的地方在於，資訊偽裝的主要目的是將真正重要的祕密訊息藏在掩護媒體。除了不希望讓人發現掩護媒體中有額外訊息之外，在應用上最主要的目的則是資料嵌入量的多寡；資料嵌入量愈高才愈有實用價值。

　　本篇論文即為針對三維模型資料而設計的超高容量資訊偽裝演算法：包括了一個資料格式域的資訊偽裝演算法及一個空間域的資訊偽裝演算法，這兩個演算法皆能達到遠高於以往的資料嵌入量；而且這兩個方法皆可以獨自執行，也可以共同使用在同一組三維模型資料上而達到更大的資訊偽裝容量。

Transmitting digital media over networks has become very convenient and popular in recent years. Therefore, information hiding in multimedia has drawn a lot of attention and has become an important research issue. A message is hidden in digital media such as images, videos, audios, documents or 3D polygon models in an imperceptible manner. This is done so as not to impede host media use, while information hiding can be helpful for various interesting applications such as covert communications and watermarking for ownership authentication and content protection. A single information hiding scheme cannot be suitable for all of these applications due to their incompatible goals. In this thesis, we concentrate on information hiding, or “steganography”, on 3D polygon models for covert communications. How to exploit the geometric characteristics of 3D models to provide high-capacity data hiding is the main task in this thesis.

In this thesis, we hide messages in both spatial domain and representation domain. In representation domain, an ultrahigh-capacity distortion-free information hiding algorithm for 3D polygon models is presented. We propose a novel embedding approach to embed messages in the representation domain of 3D polygon model using the proposed rearrangement approach in distortion-free manner. In contrast to the general data hiding schemes which embed messages by slightly modifying the appearance of the cover media, the proposed approach does not hide messages in the vertex coordinates/normals of cover model, therefore, will not change the appearance of the cover model, i.e., distortion-free. Furthermore, the proposed approach can hide very high capacity (above 9 bits/per vertex) in the representation domain. Experimental results show that the cover and stego models are still identical as the volume of embedding messages is up to 20 bits/per vertex. In the spatial domain, a very high-capacity, information-hiding algorithm based on a novel multi-layered embedding scheme for 3D polygon models is presented. The proposed approach can hide 3(|V|-3)n_layers bits on a polygon model ( |V| represents the number of vertices and n_layers represents the number of hiding layers); while the upper-bounded distortion can be limited to I (I represents the width of a partitioning interval). Experimental results show that the proposed approach can provide much higher hiding capacity than other state-of-the-art approaches, while obeying the low distortion and security basic requirements for steganography.

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