數位浮水印技術屬於信息隱藏領域，最近已經出現了大量的研究興趣。它在各種應用領域已成為重要的一門技術。數位浮水印用於內容保護，版權管理，內容認證和篡改檢測水印等。然而在嵌入數位浮水印的同時，往往需要考慮到實現數位影像的強健性和真實性。在過去的幾年裡，已有許多作者提出各種數位浮水印的技術。
目前最主要可以分成兩個研究領域:一種是將資訊隱藏在圖像的空間域(Spatial domain)裡，另一種是將資訊藏在圖像的頻率域(Frequency domain)中。現今數位浮水印技術發展在頻率域中較為廣泛且有較好的隱蔽性，因此在本文中，我們以過去文獻上所提及在頻率域上嵌入浮水印的技術為基礎，如建構在離散餘弦轉換以及離散小波轉換來實現數位浮水印系統等。
在資訊的強韌性表現下，無論在哪一種頻率域方法去實現數位浮水印技術所得的強韌性都各有優勢以及不足的地方。在本篇論文中，我們提出了複合式浮水印技術，其做法即是結合了兩種頻率域的嵌入方法，例如離散餘弦轉換以及離散小波轉換，透過這樣的想法我們可以得到在兩個轉換域上的隱密資訊，因此在影像遭受到惡意攻擊時，在做浮水印偵測時能保留在兩種轉換域上的資訊，能對我們在做著作權保護上有更進一步截長補短的效用。此後，經由一些實驗，包含: 壓縮、切割、縮放、平滑處理、雜訊、旋轉、平移以及複合式攻擊後，顯示我們的方法達到一定程度的隱蔽性及強韌性。
在浮水印設計和檢測浮水印表現是本篇論文的一大突破。藉由計算出真陽率(True positive rate)及假陽率(False positive rate)利用在展頻技術和SVM(Support Vector Machine)方法上我們可以得到ROC (Receiver Operating Characteristic)曲線，這將會幫助我們判別浮水印機制表現的好壞。

Digital watermarking, a branch in the field of information hiding, has drawn lots of attention of researchers and has become an important technique in various application areas. Watermarking has been widely used for content protection, copyright management, content authentication and tamper detection etc. Various kinds of watermark techniques have been proposed in the past decade, and a key problem of this issue is how to balance the tradeoff between watermark robustness and the fidelity of images.
Based on the way to embed the watermark sequences, existing techniques can be categorized into two fields: one is to embed the watermark in spatial domain directly, and the other is to hide it in the frequency or transform domains. Today, digital watermarking techniques with better confidentiality are those developed in transform domains. Hence, in this thesis, we adopt typical transformed-based watermarking methods, such as based on DCT- and DWT-based schemes, to design and implement our watermarking algorithm.
As for the robustness issue, we have to recognize that no matter how the robustness is measured, the pros. and cons. of a transform-based watermark scheme depends on the characteristics of the transform it used. In this thesis, we propose a joint watermarking technique and derive the way to “integrate” two independent watermarking approaches, such as DCT- and DWT-based ones. With this idea we can ensure the hiding data would be found in both transform domains without interference. Meanwhile, we will show that even the host data suffered from malicious attacks, our watermarks can still be detected in at least one of the transform domains; that is to say, they could be complement to each other. Finally, several experiment results, including JPEG compression, cropping, scaling, Gaussian noise, rotation, translation, composite attacks, stirmark and so on, will show that the proposed method has good performances on confidentiality and robustness.
The breakthroughs of our work are the watermark derivation and the watermark detection performance strategy. By calculating the true positive rate and false positive rate we show the ROC curve utilizing Spread Spectrum and SVM method, so that they will help us to diagnose the performance of our watermarking scheme.

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