在本篇論文中，我們提出軟式萃取子區塊極性之金匙視訊浮水印系統，此系統建構於MPEG-2上能同時完成浮水印嵌入與視訊壓縮。浮水印雖僅嵌入於I畫面，卻會經由移動預估編碼機制傳播到P與B畫面中，因此在萃取端提出兩種考慮視訊時間軸上相關性的權重計算方式，以之參考所有畫面資訊，視訊群組為單位軟式萃取子區塊極性來解得浮水印。 我們將浮水印嵌入在低頻離散餘弦係數。低頻係數首先合成子區塊，以區塊極性選出適合加入浮水印的區塊，區塊極性並且和浮水印進行Tri-state XOR（TXOR）的運算以產生金匙。金匙記錄浮水印嵌入的區塊位置，因此在萃取端能取代原始視訊訊號，與區塊極性進行TXOR運算即可解出浮水印。 實驗結果顯示此視訊浮水印系統具有良好的透明度，嵌入浮水印的畫面其PSNR值與未嵌入者相近，而萃取端參考所有種類畫面的資訊軟式萃取子區塊極性的確能夠提升浮水印的強韌性。 In this thesis, we propose a key-based video watermarking system in which the watermark embedding and the video encoding are processed at the same time on MPEG-2. Since the watermark information would propagate to P/B frames through the motion compensated coding, the watermark is embedded in a single I frame but can be extracted from all frames in the same group of pictures (GOP). The watermark is embedded in the low frequency DCT coefficients based on the block polarity. The block polarity is operated with the watermark by Tri-state XOR to generate the secret key, which labels the block locations of the embedded watermark. In the decoding end, the key is operated with the block polarity by Tri-state XOR to get the extracted watermark from all kinds of frames. Finally, the watermark over a GOP can be calculated by a weighted voting procedure according to the frame types and the displacements of the pixels. The simulation results show that the system has great imperceptibility that the PSNR of the watermarked frames are almost the same as the un-watermarked and more accurate normalized correlation (NC) can be obtained as well.
