(t, n)門檻式機密影像分享技術是將機密影像分成n張無意義的分享影像並分配給n位參與者，其中任何超過t位參與者的群組，都能利用他們的分享影像還原機密影像。反之，則不能還原機密影像。同時，為降低分享影像的顯著性，可進一步藉由偽裝學(Steganography)技術，將分享影像藏入有意義的掩護影像中形成一張偽裝影像，來避免攻擊者的注意力與提供管理上的便利性。本文提出結合偽裝學技術的可逆機密影像分享技術，讓參與者在還原過程中，除了可以從偽裝影像中擷取機密影像外，還可以將偽裝影像回復成掩護影像。本文採用m進位下之差值擴張方法配合m進位的機密影像分享技術，可以得到高嵌入量及高影像品質之無失真影像秘密分享技術。實驗結果顯示，本論文所提出的方法，偽裝影像有良好的品質且掩護影像有很高的嵌入量。

Conventional (t, n) secret image sharing scheme shares a secret image to shared images and secret keys. Collecting t shared images corresponding with their secret keys recovers the secret image. However, noise-like shared images always attract attackers attention. Therefore, embedding shared images to meaningful cover images to form stego images can efficiently reduce attackers attention. This paper presents a different-expansion based reversible secret image sharing technique to let participants restore the secret image and cover image in recovering procedure. The proposed scheme can further raise the embedded capacity when the cover image does not need to be perfectly reconstructed. Experimental results show each stego image have good image quality and high embedded capacity.

目錄  
第一章 緒論	                         1
1.1	研究背景與動機	                 1
1.2	研究目的與方法	                 4
1.3	論文架構	                         5
第二章 相關文獻探討	                         7
2.1	機密分享技術	                 7
2.1.1	Shamir(t, n)門檻機制	         7
2.1.2	Thien和Lin所提之方法	         8
2.1.3	Lin和Chan所提之方法	         9
2.1.3.1 分享與偽裝階段	                10
2.1.3.2 還原階段	                        11
2.2	差值擴張法	                12
2.2.1	Tian的方法	                12
2.2.2	Yi的方法	                        15
第三章 基於差值擴張之可逆機密影像分享技術	19
3.1	分享階段	                        20
3.2	嵌入階段	                        22
3.3	擷取與還原階段	                26
第四章 實驗結果與分析比較	                29
4.1	實驗結果	                        31
4.2	分析比較	                        35
第五章 結論	                        39
參考文獻	                                40
附錄-英文論文	                        43

圖目錄
圖2.1 分享圖大小比較	         9
圖2.2 可逆式資訊隱藏技術	        12
圖3.1 分享階段流程圖	        20
圖3.2 嵌入方法示意圖	        22
圖3.3 嵌入階段流程圖	        23
圖3.4 擷取與還原階段流程圖	        26
圖4.1 機密影像(256x256)	        29
圖4.2 掩護影像(512x512)	        30
圖4.3 各種不同類型偽裝影像之品質	33
圖4.4 不同的t之嵌入量比較-1(m=7)    36
圖4.5 不同的t之嵌入量比較-2(m=7)	37
圖4.6 不同的t之嵌入量比較-3(m=7)    38

表目錄
表4.1 不同偽裝影像的品質(m=7)	                31
表4.2 不同的m之分享影像大小及PSNR之關係(以Lena圖為例)	32
表4.3 不同m之最大嵌入量與PSNR(以Lena圖為例)	        32
表4.4 本方法與其他方法比較	                        35

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