可逆的浮水印技術可以將嵌入浮水印的影像擷取出資訊並無失真的還原，它是利用相鄰像素間的高度關連性。應用的範圍包括軍事和醫療影像。而在浮水印嵌入的過程中會發生像素值溢位的問題。因為像素值的範圍可能會超過 [0:255]的範圍，大部份需要一個位置圖來解決這個問題。
在這個研究裡，我們提出了一個不需要位置圖的可逆浮水印演算法，首先計算出一個預測門檻值，值方圖橫移的方法是基於這個門檻值來解決溢位問題，接這採用另一個門檻值來達到容量控制，這樣一來圖片在不同的嵌入容量下可以有更好的品質。
實驗結果顯示我的提出的方法較 FUJIYOSHI 的方法在相同容量下有更高的PSNR值，影像品質的PSNR 平均高約 3 dB。且我們的方法提供更高的嵌入容量。

Reversible watermarking techniques enable the extraction of the embedding bits from a watermarked image in a lossless way. It exploits the high spatial correlation among neighboring pixels. Application in reversible watermarking includes military and medical images. However, images occurs overflow or underflow problems during the imbedding process. Since pixels value may out of range between [0:255]. Most methods require a location map to solve such problems.
In this study, we propose a location map free reversible watermarking algorithm, firstly a prediction threshold value is computed, histogram shifting scheme based on the prediction threshold value to solve overflow and underflow problems, secondly another threshold value is adopted to achieve capacity control, image quality is better in different payload length with this control.
The experimental results reveal that the performance of our proposed method outperforms that proposed by FUJIYOSHI et al. For example, with the same imbedding capacity, the PSNR of our scheme is higher than FUJIYOSHI et al. about 3 dB. Furthermore, our algorithm provides higher embedding capacity compare with FUJIYOSHI et al.

中文摘要 i
Abstract ii
Content iii
List of Figures iv
List of Tables vi
Chapter1. Introduction 1
1.1. Watemarking introduction 1
1.2. Motivation and objectives 4
1.3. Organization of the Thesis 6
Chapter2. Related Works 7
2.1. Reversible watermarking schemes 7
2.1.1 Reversible watermarking schemes using difference expansion 7
2.1.2 Reversible watermarking schemes using histogram shifting 8
2.1.3 Reversible watermarking using prediction-error and histogram shifting 9
2.2. Location-map free reversible watermarking schemes 10
Chapter3. Proposed Method 12
3.1 Prediction value and prediction error 13
3.2 Prediction threshold value 15
3.3 Predicted threshold value and predicted value 16
3.4 Histogram shifting scheme 18
3.5 Modification of predicted value in half plane2 21
3.6 Maximum of threshold value k 22
3.7 Embedding and Extraction 24
3.7.1 Embedding process 24
3.7.2 Extraction process 26
3.7.3 Avoiding multilayer embedding 28
Chapter4. Experimental results 29
Chapter5. Conclusion and Future Work 32
Reference 34

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