以小波為基礎並利用雙浮水印與人類視覺系統之多功能彩色浮水印技術

Abstract

本論文中，我們提出一套完整的數位浮水印架構，以同時解決數位內容所有權保護與驗證之議題，我們將可視與半易碎型浮水印(雙浮水印)結合並嵌入彩色圖片數位內容之中，可視浮水印將對所有權保護產生效用，半易碎型浮水印則在驗證浮水印圖片的完整性與一致性，防止有心人對可視浮水印圖片進行破壞，使其失去所有權保護之效能。 在設計可視浮水印系統時，比較重要的條件和需求為半透明性與強韌性，但這兩者互為取捨，本研究中，我們發現人類視覺系統 HVS (Human Visible System)-對比敏感函數 CSF (Contrast Sensitive Function) 與 雜訊可見函數(Noise Visibility Function) 可以在兩者之間取得一個適當的平衡點，透過CSF與NVF可以得知圖片全域與區域性的特性以便進行可視浮水印的嵌入，同時加入小波雜訊可視門檻值(DWT Noise Visibility thresholds) 調整浮水印加入的權重，使可視浮水印有較佳的視覺效果並兼任強韌性。在半易碎型浮水印系統中，此演算法可以正確判斷竄改之位置，並可以容忍無意間的攻擊類型(例如:JPEG壓縮與Additive White Gaussian Noise 加成性白色高斯雜訊)，達到驗證之功能。實驗結果顯示，我們產生出來的可視浮水印圖片比其他提出演算法有較好的視覺品質並有較佳的強健性，對於近年藉由影像重建理論(Image Recovery)抹除可視浮水印，也有較佳的抵抗能力。

In this study, we propose a complete architecture based on digital watermarking techniques to solve the issue of copyright protection and authentication for digital contents. We apply visible and semi-fragile watermarks as dual watermarks where visible watermarking is used to establish the copyright protection and semi-fragile watermarking authenticates and verifies the integrity of the watermarked image. In order to get the best tradeoff between the embedding energy of watermark and the perceptual translucence for visible watermark, the contrast-sensitive function (CSF) and noise visible function (NVF) of perceptual model is applied which characterizes the global and local image properties and identifies texture and edge regions to determine the optimal watermark locations and strength at the watermark embedding stage. In addition, the perceptual weights according to the basis function amplitudes of DWT coefficients is fine tuned for the best quality of perceptual translucence in the design of the proposed watermarking algorithm. Furthermore, the semi-fragile watermark can detect and localize malicious attack effectively yet tolerate mild modifications such as JPEG compression and channel additive white Gaussian noise (AWGN). From the experimental results, our proposed technique not only improves the PSNR values and visual quality than other algorithms but also preserves the visibility of the watermark visible under various signal processing and advanced image recovery attacks.