本論文提出幾種以離散小波轉換為基礎的盲目浮水印技術。在浮水印技術的研究中，嵌入浮水印後的影像品質與浮水印的強韌性一直是在這個領域研究的課題。將浮水印藏在影像頻率域中的低頻帶的重要係數，經研究可使浮水印較具強韌性來抵抗外部影像處理攻擊，但也因此犧牲影像的品質。除此之外，這些被選擇的重要係數在經量化後，很難得知其原來係數大小的排列，進而不需原始影像或浮水印的輔助以盲目的方式取出浮水印。在此篇論文中我們將分別提出以區塊（block-based）或小波樹(wavelet tree)的方式將浮水印藏入各區域中的兩個重要係數中，藉由調整的兩個重要係數間的差異來表示二元浮水印。因為此統計上差異，浮水印可以盲目被取出而不需原始影像或浮水印的輔助。我們也突破以往將浮水印藏入重要係數的方式，提出一種將浮水印藏入在小波樹中最不重要係數的方法來提高嵌入浮水印後影像的品質。我們利用兩個最不重要的係數的差異來表示嵌入浮水印的位元。因為小波樹中的重要係數與非重要係數皆可被使用來嵌入浮水印。我們更進而利用隨機選取重要或不重要係數來決定浮水印嵌入的位置，來提高浮水印的安全性；此外，也可同時量化重要與不重要係數的方式將小波樹一次藏入二個浮水印位元來提高可嵌入浮水印的數量。從實驗的結果可以證明，我們提出的方法具有好的強韌性與影像品質。

In this dissertation we propose some watermarking methods based on discrete wavelet transform (DWT). In the previous work, the quality of watermarked image and robustness of watermark are the topic for study in the field of watermarking. The watermark is embedded in the significant coefficient in the low frequency was found to be robust, but the watermarked image is easily visible distortion. Besides that, it’s very hard to know the permutation of original coefficients after these important coefficients were quantified. Therefore it can extract the watermark by using the blindness method and does not require the original image or the help of watermark.
In this dissertation, we first present some block-based and wavelet tree based watermarking methods. The watermark is embedded into the two localize significant coefficients. The difference between these two localize significant coefficients is modified to represent a binary watermark. Owing to the statistical difference between the two localize significant coefficients, a watermark can be effectively extracted without requiring any original image of watermark. We also propose a watermarking method that embeds the watermark into the insignificant coefficient. The method is different from previous researches which used significant coefficients to embed a watermark and it can improve the quality of the watermarked image. Since the watermark can be embedded into either significant or insignificant coefficient, we further use different combinations of significant and insignificant coefficients to embed a watermark bit to increase the security of watermarking. Furthermore, we utilize both significant and insignificant at the same time to embed two watermark bits to achieve high embedding capacity. Experimental results show that the watermarked image looks visually identical to the original and the watermark can be effectively extracted upon image processing attack.

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