網路多媒體數位浮水印及其應用之研究

Abstract

在本論文中，我們提出了一種用於影像的浮水印技術以及一種用於視訊的指印技術，並將之應用於一個以網頁為基礎的多媒體新聞資料庫系統。由於影像的漸進傳輸在許多應用中均相當重要且常用，特別是在網際網路上傳輸影像時。另一方面，複製及傳輸數位影像變得容易，使得利用數位浮水印技術來嵌入版權資訊的需求應運而生。因此，在本論文中，我們提出一個用於漸進影像傳輸的浮水印方法。此方法可以在影像仍在傳輸的過程中，即可偵測部份的浮水印資訊。隨著傳輸的進行，所取出的浮水印，其錯誤的位元數也會逐漸減少。此方法不僅能在影像傳輸的過程中，漸進地偵測浮水印，也會針對不同的係數大小，適當的選取修改值來嵌入浮水印。因此能有效降低嵌入浮水印後影像品質上的損失。

我們也提出了一個新的視訊加密與指印嵌入方法。此方法包含兩部份：(1) 伺服器端視訊加密，及 (2) 客戶端指印嵌入。首先，伺服器將一段視訊加密並以群播方式傳送給所有客戶端。接著，利用(v, k, 1)-BIBD來將解密金鑰分解成v = O(sqrt(n))把解密子金鑰，並群播給n個客戶端。在收到各自的解密金鑰後，每個客戶端便可組合他們各自的解密子金鑰，得到一把嵌入指印後的解密金鑰。當使用這把金鑰來解開加密的視訊後，便會在視訊中嵌入一個對應於該客戶端的指印。通常嵌入指印會使視訊中產生若干雜訊。由實驗結果發現，當指印由15個以下的浮水印組成，或浮水印強度小於0.5時，畫面的訊噪比(PSNR)即高於35db。故本技術極適合用於網路環境中的視訊著作權保護。

最後，我們整合數種多媒體資訊擷取技術，建立了一個多媒體新聞網站。其中所使用到的技術包括針對新聞標題、主播與過場，進行語音、影像與視訊分析，以建立一個有組織、有意義的新聞視訊摘要。讓使用者可以利用非循序、快速而具彈性的方式來瀏覽大量的新聞資料。藉由聲音分析，我們可以將新聞節目分成新聞片段與廣告片段。利用2003年七月至2004年8月間的400小時電視新聞做為實驗資料發現，本方法具有96%的正確率。我們並使用OCR技術來辨視銀幕上的新聞標題或子標題，做為每段新聞故事的文字資訊。此外，所抽取出的新聞標題也可以用在網路上的相關新聞的連結與導覽。藉由整合人臉與場景分析與辨識技術，OCR的結果可用來提供使用者針對特定新聞的多種查詢。

我們也將所發展的浮水印與指印技術實際用於所建立的多媒體新聞資料庫中。在關鍵畫面的抽取過程中，浮水印系統會為每個畫面嵌入浮水印以保護內容擁有者的著作權。此外，換鏡偵測的結果可以提供給指印系統，做為更新客戶端指印的時間點，以增強所嵌入指印的強固性。在多媒體的應用中，演算法的效能是一項重要的課題。由測試結果發現，我們所提出的浮水印與指印方法，均極適合於網路上的各種多媒體應用。

In this dissertation, we propose a progressive image watermarking scheme and a video fingerprinting scheme for copyright protection of multimedia applications on the Internet. The ease of transmission and copying of images creates the need to use digital watermarking to embed the copyright information seamlessly into the media. On the other hand, progressive transmission of images is very useful in many applications, especially in image transmission over the Internet. Since the progressive image transmission has been widely used, in this dissertation, we first propose a progressive image watermarking scheme. In this scheme, the watermark is embedded in such a way that we can retrieve part of it even when the watermarked image is still being transmitted. As transmission progresses, the retrieved watermark has a decreasing bit error rate. Our proposed method can not only detect the watermarked image progressively, but also intelligently select watermark embedding locations and is robust to various attacks.

We also propose a new video scrambling and fingerprinting approach for digital media right protection. The proposed method contains two parts: (1) video scrambling at server side, and (2) fingerprint embedding at client side. First, a content server scrambles and multicasts video contents to end users. Then, by applying a (v, k, 1)-BIBD scheme, the server partitions a descrambling key into v=O(sqrt(n)) descrambling subkeys, and multicasts to n users. On receiving descrambling subkeys from the content server, each user combines descrambling subkeys into a descrambling key embedded with a fingerprint. By using he's descrambling key, a scrambled video becomes a fingerprinted video designated to the user.According to the experiment results, when the fingerprint consisting of less than 15 watermarks or watermark strength a s less than 0.5 the PSNR of video frames can be 35 or higher. Thus, this approach is suitable for multimedia applications over The Internet.

Finally, an integrated information mining techniques for multimedia TV-news archive is addressed. The utilized techniques from the fields of acoustic, image, and video analysis, for information on news story title, newsman and scene identification. The goal is to construct a compact yet meaningful abstraction of broadcast news video, allowing users to browse through large amounts of data in a non-linear fashion with flexibility and efficiency. By using acoustic analysis, a news program can be partitioned into news and commercial clips, with 90% accuracy on a data set of 400 hours TV-news recorded off the air from July 2003 to August of 2004. By applying speaker identification and/or image detection techniques, each news stories can be segmented with an accuracy of 96%. On screen captions or subtitles are recognized by OCR techniques to produce the text title of each news stories. The extracted title words can be used to link or to navigate more related news contents on the WWW. In cooperation with facial and scene analysis and recognition techniques, OCR results can provide users with multimodality query on specific news stories. Some experimental results are presented and discussed for the system reliability and performance evaluation and comparison.

The proposed web based TV news archive was also used as a test bed of the proposed image watermarking and video fingerprinting methods. Watermarks can be embedded automatically when key frames of a news story are extracted, and information obtained from video analysis process can be used to increase the robustness of video fingerprinting. In multimedia applications, computational efficiency is one of the important issues. Our testing shows that the proposed watermarking and fingerprinting methods are efficient to real world applications.