臺灣博碩士論文加值系統

中文摘要
本論文提出了一個新的Steganography方法，利用DWT (Discrete Wavelet Transform)轉換後的特性，將秘密訊息分別藏入其中三個子頻帶中。利用這三個子頻帶分別代表水平邊緣、垂直邊緣及對角邊緣的特性，可提高藏密後的影像品質。本論文分成了兩種mode共五種case來討論，藉由藏入三個子頻帶中不同的LSBs (Least Significant Bits)位置以提供不同的藏入量。至於安全性問題，若無 ”Key matrix” 便無法恢復至藏密後的狀態，加上藏入的訊息為做過運算分類後的訊息，所以直接取出子頻帶中的最右邊幾個LSBs並無法將其正確無誤的還原為原始的訊息。

Abstract
In this thesis, we proposed a novel stegangraphy method utilizing the features obtained from Discrete Wavelet Transform (DWT). Applying a secure coding scheme, the secret messages are embedded into the three high frequency sub-bands of DWT coefficients. Since the portion which human eyes are sensitive to, the low frequency sub-band, remains unaltered, the image quality after secret messages embedding is increased. According to different needs of embedding capacity, we explain the embedding method in five cases. In addition to high embedding capacity and image quality, the proposed approach provides respectable security as well. Because the original secret messages are arithmetically manipulated before embedding, they would not be recovered directly from the rightmost Least Significant Bits (LSBs) of coefficients in any sub-band.

Table of contents
Chapter1 Introduction 1
1.1 Background and objective 1
1.2 Motivation 2
1.3 Paper architecture 3
Chapter 2 Bibliography discussion 4
2.1 Relative background and categorization 4
2.2 Relative theories and bibliography review 7
Chapter 3 Proposed method 15
3.1 Embedding procedure 15
3.1.1 Varying mode 16
3.1.2 Fix mode 21
3.2 Extracting procedure 25
3.2.1 Varying mode 25
3.2.2 Fix mode 28
Chapter 4 Simulation results and analysis 31
4.1 Simulation results 32
4.1.1 Varying mode 32
4.1.2 Fix mode 33
4.2 Performance analysis 34
Chapter 5 Conclusions and future works 40
5.1 Conclusions 40
5.2 Future works 40
References 41
Appendix 41


List of tables
Table 1 Sequence mapping table 17
Table 2 Capacity of 6 images in 3 cases (varying mode) 33
Table 3 PSNR of 6 images in 3 cases (varying mode) 33
Table 4 Capacity of 6 images in 2 cases (fix mode) 34
Table 5 PSNR of 6 images in 2 cases (fix mode) 34
Table 6 Capacity and PSNR of literature [9] 35
Table 7 Capacity and PSNR of literature [14] 35
Table 8 Capacity and PSNR of literature [15] 36
Table 9 Comparison with literature [9] and [14] 36
Table 10 Comparison with literature [9] and [14] 37
Table 11 Comparison with literature [9] and [14] 37
Table 12 Comparison with literature [15] 38


List of figures
Figure 2-1 Three kind images 7
Figure 2-2 Weighting of an 8-bit pixel 9
Figure 2-3 Three kinds of side-match proposed in [15] 11
Figure 2-4 The horizontal operation 12
Figure 2-5 The vertical operation 12
Figure 2-6 First-order Haar-DWT result 13
Figure 2-7 Quantization table in [20] 13
Figure 3-1 Raster-scan order 17
Figure 3-2 Embedding status (varying mode, case 1) 18
Figure 3-3 Embedding status (remaining bits) 19
Figure 3-4 Key matrix 19
Figure 3-5 Embeddimg status (varying mode, case 2) 20
Figure 3-6 Embeddimg status (varying mode, case 3) 21
Figure 3-7 Embedding status (fix mode, case 1) 23
Figure 3-8 Embedding status (fix mode, case 2) 24
Figure 3-9 Extracting status (varying mode, case 1) 26
Figure 3-10 Extracting status (remaining bits) 26
Figure 3-11 Extracting status (varying mode, case 2) 27
Figure 3-12 Extracting status (varying mode, case 3) 27
Figure 3-13 Extracting status (fix mode, case 1) 29
Figure 3-14 Extracting status (fix mode, case 2) 30
Figure 4-1 Six cover-images 32

References
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