基於小波樹分群調變之差動能量浮水印技術

Abstract

差動能量浮水印技術 DEW (Differential Energy Watermarking) 與小波樹量化浮水印技術 WTQ (Wavelet Tree Quantization) 係利用能量差異化嵌入數位浮水印資訊之代表性技術。由於此二者僅利用能量消除之技巧隱藏保護數位影像之著作權資訊，故易受一般資訊隱藏分析浮水印消除之攻擊，因而其安全性已遭多位研究學者質疑。本論文提出小波樹分群調變浮水印技術 WTGM (Wavelet Tree Group Modulation)，研製之目的在於利用小波樹遍佈較大空間區域之資料結構、子集合和 (sum-of-subsets) 之能量集合特性，以及正負調變 (positive/negative modulation) 之優異能量區隔與攻擊抵抗能力，改善小波樹量化浮水印技術 (WTQ) 低安全性及低偵測值之缺點。同時，本研究亦加入人類視覺系統 HVS (Human Visual System)－對比敏感函數 CSF (Contrast Sensitive Function) 與雜訊可見函數 NVF (Noise Visibility Function)，使得小波樹分群調變浮水印技術 (WTGM) 具有較佳的視覺效果與不可察覺性。實驗結果顯示，小波樹分群調變浮水印技術 (WTGM) 可有效地抵抗一般常見數位影像處理攻擊與小幅度幾何扭曲攻擊，嵌入之浮水印並具有不易分析、移除之高度安全性。

DEW (Differential Energy Watermarking) and WTQ (Wavelet Tree Quantization)-based watermarking algorithms are two representative techniques using energy difference for copyright protection and ownership verification. Since both watermarking algorithms are vulnerable to general cryptanalysis, their robustness or security is suspected by watermarking researchers. In this thesis, we present a differential energy watermarking algorithm based on the wavelet tree group modulation structure, i.e. WTGM (Wavelet Tree Group Modulation). The DWT image is divided into disjoint super trees (each super tree containing two sub-super trees). The watermark is embedded in the relatively high-frequency components using the group strategy such that energy of sub-super tree A and that of sub-super tree B are close. The employment of wavelet tree structure, sum-of-subsets and positive/negative modulation effectively improve the drawbacks of the WTQ scheme for its insecurity and lower detector response. The consideration to the CSF (Contrast Sensitive Function) and NVF (Noise Visibility Function) of the HVS (Human Visual System) provides a better visual effect of the watermarked image. The experimental results demonstrate the effectiveness of our algorithm in terms of robustness and imperceptibility.