資訊隱藏技術是結合了密碼學技術與數位多媒體處理的重要研究領域。這些技術可廣泛應用於數位多媒體，特別是數位影像。其中基於錯誤改正碼的資訊隱藏技術，可以提高信息嵌入率並同時減少修改的位元數目。目前為止，基於錯誤改正碼的資訊隱藏技術的文獻已有很多，研究者們提出了大量有特定功能的各種方案。例如，使用漢明碼、BCH碼、Golay碼等錯誤改正碼的信息隱藏技術，其中部份是探討可逆式的資料隱藏。所謂可逆式資料隱藏，是取回隱藏資料後可同時將原載體恢復到原來的狀態。
最近，Jana等人提出了基於（7, 4）漢明碼的部分可逆數據隱藏（Partial Reversible Data Hiding）。Jana等人的機制有三個影像：原始影像（Original Image; OI），封面圖像（Cover Image; CI）和偽裝圖像（Stego Image; SI）。稍微修改OI獲得CI (註:CI與OI幾乎相同)，之後將秘密藏入CI生成SI。所謂的部分可逆式資料隱藏是我們可以無損失地重建CI。然而，在Jana等人的PRDH中，作者僅通過使用具有偶數（或奇數）校驗的（7, 4）漢明碼來調整冗餘位元。這種簡單的方法在7個最低有效位元 (Least Significant Bit; LSB)中會最多會修改3個冗餘位元來從OI獲得CI，這嚴重降低了CI影像品質。
在本文，我們提出了兩個方案：第一個機制可增強CI的影像品質，從而提高了部分可逆性的效果。第二個機制則提高了嵌入高容量。另外，文中我們也對這些方案的均方差(Mean Square Error; MSE ) 做了理論估算，證明我們的機制比。Jana等人的機制有較佳的優勢。

Data hiding (DH) technology is an important research field that combines cryptography and digital multimedia processing. DH can be widely used in multimedia, especially digital images. Error correcting code (ECC) based DH can is increase embedding capacity, and meanwhile reduce the number of modified bits. Up to present, there were many researches on ECC based DHs, e.g., using Hamming code, BCH code, and Golay code. Some of these DHs are the reversible data hiding (RDH). RDH allows the recipient for extracting secret data and meantime restore the original cover media.
Recently, Jana et al. proposed a partial RDH (PRDH) based on (7, 4) Hamming code. Their scheme deals with three images: the original image (OI), the cover image (CI), and the stego image (SI). The CI is generated by slightly modifying OI (both OI and CI have almost the same image quality). After that, one can embed secret into CI to generate SI. The so-called partial reversible capability is that we can reconstruct the CI without distortion. However, in Jana et al.’s PRDH, the authors only adjust redundant bits by using (7, 4) Hamming code with even (or odd) parity. This simple approach may modify 3 redundant bits at most in 7 least significant bit (LSBs) for generating CI from OI, and this degrades the CI quality seriously.
In this thesis, we construct two schemes: the proposed PRDH (PPRDH) and the modified PRDH (MPRDH). PPRDH enhances the partial reversible property that improves the visual quality of CI. On the other hand, MPRDH enhances PPRDH to achieve the high embedding capacity. Theoretical estimations of average mean square errors for these PRDH schemes are given to demonstrate the advantage of our PRDH schemes.

Chapter 1 Introduction 1
1.1 Background 1
1.2 Contribution of the Thesis 3
1.3 Organization of the Thesis 3
Chapter 2 Previous Works 5
2.1 Hamming Code 5
2.2 Jana et al.'s PRDH 6
Chapter 3 Design Concept and Observation 11
3.1 Design Concept 11
3.2 Observation 12
Chapter 4 The Proposed Schemes 15
4.1 The Proposed PRDH(PPRDH) 15
4.2 The Modified PRDH(MPRDH) 15
4.3 Theoretical Estimation of PSNR 18
Chapter 5 Experiment and Comparison 25
5.1 Experimental Results 25
5.2 Comparison 26
Chapter 6 Conclusion and Future Work 33

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