臺灣博碩士論文加值系統

本文擬以離散小波轉換(Discrete Wavelet Transform, DWT)為工具，進行資訊隱藏之理論探討，並由實驗結果來分析影像品質(PSNR)、與藏匿容量(Capacity)等重要評估參數之改良與妥協。
由於DWT的特性是能把原始影像資料區分為低頻與高頻的部分，而人類肉眼對低頻訊號較為敏感。因此本論文所提出的一個資訊隱藏技術方案，是針對做完DWT轉換後的小波係數直接進行資訊隱藏的動作，其優點有： (1)充分利用DWT之特性，將欲隱藏之重要資訊嵌入肉眼較不敏感的高頻帶，而盡量保持低頻係數之完整性，以提升影像品質。 (2)在維持一定程度影像品質的前提之下，將可藏入更大容量的重要資訊而不被發覺，以達成資訊安全的功能。 (3)可依據使用者的需求來動態調整所需的藏匿容量。

In this thesis, performing image steganography on frequency domain in stead of spatial domain is analyzed. Image steganography is a new data hiding scheme which protects the essential information embedded in an image. The objective is to hide as many bits as possible while maintaining certain image quality (in terms of Peak Signal-to-Noise-Ratio, PSNR). By embedding the essential information in the high frequency parts of the DWT coefficients and keep the low frequency part unchanged, we can exploit the characteristic of DWT and protect the embedded information more securely since human eyes are much less sensitive to high frequency signals. Furthermore, the proposed scheme allows the users to dynamically modify the embedding capacity according to their own applications.

Chapter 1 Introduction 1
1.1 Background 1
1.1.1 Cryptography 2
1.1.2 Information hiding 2
1.1.3 Steganography 4
1.1.4 Watermarking 4
1.2 Motivation 5
1.3 Organization of thesis 6
Chapter 2 Related works 7
2.1 Relative theories 7
2.2 Literatures review 9
2.2.1 Data hiding methods in spatial domain 9
2.2.2 Data hiding methods in frequency domain 12
Chapter 3 Proposed method 16
3.1 Embedding procedure 16
3.2 Extracting procedure 19
Chapter 4 Simulation results and analysis 21
4.1 Simulation results 22
4.2 Performance analysis 23
Chapter 5 Conclusions and future works 29
5.1 Conclusions 29
5.2 Future works 29
References 30
Appendix 32

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