[[alternative]]Fragile Watermarking with Increasing Coding Efficiency for Video Authentication and Verification in MPEG-4 FGS

碩士電機工程學系[[abstract]]MPEG-4 FGS是一個有發展性的編碼規格，卻沒有合適的浮水印技術，因此本論文提出一個適用於MPEG-4 FGS (fine-granular scalability) 視訊偵測與驗證的易碎型浮水印。我們因應了FGS的特性分別在FGS的基礎層與加強層加入浮水印，目的是為了在低頻寬時保護僅被傳送的基礎層，若在高頻寬的情況下加強層允許被傳送，則能保護更為重要的加強層的資訊。在我們所提議的基礎層浮水印演算法中，在量化過後的區塊選擇一個係數加入浮水印，而加強層方面則在剩餘平面所展開而成的位元平面中擇取會被編碼的最低層位元平面，並在其中選擇一個係數加入。基本上被嵌入浮水印的係數的數目越少，對視訊的品質影響越少但不可避免的將留下安全性的缺口，在此我們用MD5雜湊函數來達到品質與安全性兼具的效果。另外在演算法中嵌入浮水印的位置選擇，我們則是將VLC的特性加以利用，獲得增進編碼效率的額外好處。從實驗結果得知，我們所提出的基礎層浮水印演算法僅使得品質平均約下降0.6dB，而加強層下降約0.5dB。而在完整性的測試方面，及使稍微變動或更改，都可輕易偵測出其改變。值得一提的是，本文所提出的浮水印方法可以進一步提升壓縮率。因此，我們所提議的演算法在不嚴重地破壞品質的前提下，的確可為MPEG-4 FGS視訊的完整性認證提供一個良好的解決方案。[[abstract]]MPEG-4 FGS is an expansionary video encoding standard. However, there is no suitable watermarking technology for detecting the integrity of a video. Therefore, this thesis presents a fragile watermarking method for video authentication and verification in MPEG-4 FGS (fine-granular scalability). We follow the FGS characteristics and then embed the watermark into the base-layer and enhancement-layer separately. The reason is that we protect the base-layer in low-bandwidth and the enhancement-layer in high- bandwidth. In the base-layer watermarking algorithm, we embed the watermark into a quantized DCT block. In enhancement-layer watermarking, we take the least bit-plane that will be encoded and choose a specific bit for embedding the watermark. We employ the VLC feature in selecting a specific bit for increasing the coding efficiency. We select a bit in a block for embedding the watermark to reduce the video quality distortion. However, if we leave most unmarked coefficients it will result in a security gap for attacks. Therefore we use MD5 in our proposed algorithm for reinforcing security. From this experiment, we know that the reduced quality with base-layer watermarking is 0.6dB on average. The average reduced quality with the enhancement-layer is 0.5dB. Our algorithm can also detect the integrity of a video after this attack test. The compression rate test shows that compression rate is improved. Consequently our proposed algorithm provides a good solution for video authentication and verification in MPEG-4 FGS