以能量調變和一致性控制為基礎之小波樹浮水印演算法

Abstract

WTQ(Wavelet Tree Quantization)為利用小波樹能量差異之特性來嵌入數位浮水印的代表性方法。根據Wang的實驗可以證明WTQ對於大多數的攻擊都具有相當良好的抵抗性。但由於WTQ方法利用能量消除和Bit-Plane Remove的方式來嵌入浮水印，因此Das和Maitra使用資訊隱藏分析的方式將浮水印消除，並提出新的架構來避免密碼分析之攻擊。但在Das 和Maitra所提出的修改架構(Modify WTQ)中，必須儲存Group排列的順序，此資訊的保存將變成一個問題。

為了改善前述之缺點，我們以小波轉換為基礎，建立一個以小波樹能量調變和一致性控制為基礎之小波樹浮水印演算法(WTW-EMCC)，此方法取出浮水印時不需要原圖和分群資訊，只需要嵌入浮水印時所使用的Seed k，便可將嵌入的浮水印取出。此外在可以儲存Group資訊的前提下，我們將會設計另一個以小波樹能量調變和一致性控制之圖片無失真數位浮水印演算法(Non-blind WTW-EMCC)，也就是在可以儲存Group資訊的情況下，我們嵌入浮水印後的圖片和原圖是完全一樣的，如此可以將圖片作最完整的保存。最後在改良了MWTQ的方法後，我們緊接著會探討不同的Group方式對於浮水印強健性的影響，如此可以使得浮水印抵抗較多種類的攻擊。

根據實驗結果，本研究所提出的兩個方法皆可以抗許多常見的浮水印攻擊(Ex. JPEG壓縮，Median filter，多重浮水印...等)，且具有不易分析和抹除的高度安全性。

WTQ (Wavelet Tree Quantization) is representative technique using energy difference for watermarks embed. According to Wang’s experiment WTQ is resistant to a variety of signal distortions. But unfortunately WTQ embedding watermark just uses energy eliminate, Das and Maitra make the cryptanalysis to eliminate the watermark, and they propose a new scheme to avoid the attack of cryptanalysis. In the scheme of Das and Maitra the information of group order is necessary, and the preserve of information is a problem. In order to improve the defect, we use wavelet tree energy modulation and consistency control (WTW-EMCC) base on wavelet transform for watermarking. The WTW-EMCC scheme doesn’t need original image and group ordering information for watermark extract, and it just need the secret seed k in watermark embedded. Furthermore if we can store the grouping information, we propose another Non-blind scheme also base on wavelet tree energy modulation and consistency control (Non-blind WTW-EMCC). The characteristic of Non-blind WTW-EMCC is lossless, and it means that the original image is the same with the watermarked image. With our scheme we can preserve the quality of image in complete. Final we will discuss how to group to obtain better robustness. The experimental results demonstrate the effectiveness of our two algorithms in terms of robustness and imperceptibility.