電腦與通訊網路的進步，使得電子文件交換、電子商務、隨選視訊、數位圖書館等數位服務蔚為風尚。但是，由於數位化資料具有容易且精確地被複製的特性，所以需要有效的保護機制來防止竊取或篡改，數位浮水印(digital watermarking)就是產學界高度重視的技術之一。數位浮水印技術為近年來新興的技術，它能將資訊隱藏於多媒體資料中用來宣告所有權、著作權或認證。
在我們的研究上，我們是使用通訊系統中的展頻通訊原理來實現數位浮水印。本文將數位浮水印系統比擬成通訊系統，原始媒體資訊(影像)之頻率域為傳輸通道，而浮水印資料為傳輸訊號，可能遇到的攻擊或破壞則視為通道雜訊[1][23]。展頻通訊已區分為直接序列展頻(Direct Sequence Spread Spectrum DSSS)與跳頻展頻(Frequency Hopping Spread Spectrum FHSS)二種，因此，我們針對這二種展頻技術而設計出跳頻展頻浮水印(FHSS Watermarking)與直接序列展頻浮水印(DSSS Watermarking)。
JPEG壓縮是現今普遍使用的壓縮格式，因它有著高壓縮特性，以及壓縮後影像品質仍很高，所以普遍被大眾使用。在本論文中，我們針對JPEG壓縮方式提出其數位浮水印的嵌入構想，將浮水印嵌入於對JPEG量化有較強抵抗力的頻帶中，以達到提高抵抗JPEG壓縮之目的。由於JPEG是使用離散餘弦轉換將影像轉換至頻率域，為了配合其特性，所以我們的展頻數位浮水印在轉換領域部分也是基於離散餘弦轉換。
實驗結果顯示，我們所提出的跳頻展頻浮水印在維持影像品質的情形下，對於JPEG壓縮具有高度的強韌性，另外使用PhotoImpact 5影像處理套裝軟體來測試比較跳頻展頻浮水印與直序展頻浮水印對各種影像處理特效其抵抗破壞效能的優劣，我們發現跳頻展頻浮水印對幾何失真破壞比較有抵抗力，而直序展頻浮水印則是訊號處理破壞具有抵抗力。
本論文最後提出融合跳頻展頻與直序展頻的Combined SS Watermarking技術。Combined SS Watermarking可同時擁有跳頻展頻浮水印與直序展頻浮水印的優點，如此，Combined SS Watermarking技術便可以抵抗較多種的破壞，達到提高數位浮水印強韌度之目的。The advances of computers and communication networks make digital content service such as digital document exchange, E-commerce, video on demand, and digital library very popular. Since digital data can be easily reproduced without any loss, copyright protection becomes an imperative requirement to prevent piracy. Digital watermarking has been proposed as one of the techniques to prevent data piracy and plagiarism. Digital watermarking is a novel and emerging technology. It has developed very quickly for the past few years. A digital watermark is a set of information that is robustly and imperceptibly embedded in the data to be protected. Applications include copyright protection, and authentication.
In the thesis, we developed two watermarking techniques using spread-spectrum technique. We interpreted the watermarking technology based on communication theory. The watermark was the signal to be transmitted. The frequency domain of the original image was the transmission channel. The attacks were regarded as channel noise. There were two methods to implement the spread-spectrum system: direct- sequence spread- spectrum (DSSS) and frequency-hopping spread-spectrum (FHSS). Based on these tow methods, we develop FHSS Watermarking and DSSS Watermarking.
JPEG compression is the most widely used image because compression technique of its high compression ratio and reasonable image quality. Here, we develop the watermark embedding method especially for JPEG encoding process since block Discrete Cosine Transform (DCT) was used for JPEG. In our approach, a block DCT-based algorithm was used to embed the image watermarking. In order to survive the JPEG compression, the watermark must be embedded in the bands that can with stand the JPEG quantization.
Experiments showed that FHSS Watermarking is more resistant to the attack of JPEG compression. The PhotoImpact 5 digital image processing software was used for other attacks. We found that FHSS Watermarking is more robust than DSSS Watermarking in geometric distortions. But in other signal processing modifications, DSSS Watermarking is more robust than FHSS Watermarking. Therefore, we developed a new method that combined with FHSS Watermarking and DSSS Watermarking, we call the new method “combined SS Watermarking”. The experimental results prove that combined SS Watermarking has both the advantages of FHSS Watermarking and DSSS Watermarking. Therefore, combined SS Watermarking is more robust and can with stand many different attacks.中文摘要……………………………………………………………...…I
英文摘要…………………………………………………………….….III
致謝
目錄
圖目錄
表目錄
第一章 緒論……………………………………………………….…….1
1.1 影像保密……………………………………………………..…1
1.2 何謂數位浮水印………………………………………………..2
第二章 數位浮水印的背景……………………………………………..4
2.1 系統設計與需求考量………………………………………….4
2.2 數位浮水印架構……………………………………………….5
2.3 數位浮水印特性……………………………………………….7
2.3.1數位浮水印之種類………………………………………..7
2.3.2浮水印影像……………………………………….……...9
2.4 影像品質定義………………………………………………..10
2.5 浮水印相似度衡量…………………………………………..11
2.6 浮水印嵌入之領域………………………………………..…14
2.7 嵌入浮水印於空間域……………………………………..…15
2.7.1 最低位元嵌入技術…………………………………...…15
2.7.2 拼湊法嵌入技術……………………………………...…17
2.8 嵌入浮水印於頻率域……………………………………...…18
2.9 展頻通訊介紹與展頻數位浮水印研究方向….……………..21
2.9.1 跳頻展頻………………………………………………...21
2.9.2 直接序列展頻…………………………………………...23
2.10 展頻數位浮水印研究方向………………………………….25
第三章 數位浮水印的破壞……………………………………………26
3.1 前言…………………………………………………...………26
3.2 JPEG壓縮影像特性簡介…………………………..…………26
3.2.1 JPEG壓縮所使用的技巧……………………..…………26
3.2.2 色相轉換……………………..………………………….27
3.2.3 取樣方式……………………..……………………..……28
3.2.4 離散餘弦轉換……………………………………….…...29
3.2.5量化……………………………………….……………….29
3.3 全域DCT與區塊DCT二者比較………………………..…..32
第四章 跳頻展頻技術之數位浮水印…………………………………34
4.1 跳頻展頻浮水印內容簡介………………………………..….34
4.2 快速跳頻展頻浮水印………………………………………...35
4.3 慢速跳頻展頻浮水印………………………………………...36
4.4 嵌入浮水印方法……………………………………………...38
4.4.1 產生跳頻碼與建立慢速跳頻表………………………....39
4.5 取出浮水一方法…………………………………………..….46
第五章 直接序列展頻技術之數位浮水印……………………………49
5.1 直序展頻浮水印內容簡述…………………………………..49
5.2 快速與慢速直序展頻浮水印………………………….….…50
5.3 嵌入浮水印方法………………………………………..…….51
5.3.1 建立慢速直序展頻表……………………………………52
5.4 人類視覺系統…………………………………….……….….54
5.5 取出浮水印方法……………………………………………...56
第六章 展頻數位浮水印強健度測試
6.1 跳頻與直序展頻浮水印壓縮強健度測試…………………...61
6.1.1 JPEG與JPEG 2000二者差異…………………………..69
6.2 影像處理與幾何破壞強韌度測試……………………….…..71
6.3 不使用原始影像取出浮水印…………………………….…102第七章 雙浮水印嵌入的展頻浮水印架構…………………………..103
7.1 融合慢速直序與慢速跳頻的復位浮水印………………….104
7.2 融合的展頻數位浮水印強健度測試……………………….107
第八章 浮水印嵌入於彩色影像技術………………………………..112
8.1 再談色相轉換……………………………………………….112
8.2 彩色原始影像嵌入浮水印………………………………….113
8.3 彩色影像數位浮水印壓縮強韌度測試………………...…..114
第九章 結論與未來工作……………………………………………..117
9.1 結論………………………………………………………….118
9.2 未來方向……………………………………………………..117
參考文獻………………………………………………………………11
