以視覺品質衡量指標應用於小波為基礎之彩色浮水印技術

Abstract

本論文中，我們提出一套可視數位浮水印架構，以解決數位內容所有權保護與驗證之議題。為了能夠設計出擁有更佳視覺效果的可視數位浮水印，我們採用以人類視覺系統為基礎的視覺品質指標。

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。為了能夠驗證以人類視覺系統為基礎的可視浮水印架構，我們利用視覺品質衡量指標VSNR(Visual Signal-to-Noise Ratio) 以及VIF(Visual Information Fidelity) 驗證可視浮水印。實驗結果顯示，我們產生的可視浮水印圖片比其他提出演算法有較好的視覺品質以及強健性，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 an architecture based on digital watermarking techniques to solve the issue of copyright protection and authentication for digital contents. In order to design better visual effect of visible watermark image, we adopt the visual quality measure based on HVS (human visual system). 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. In addition we use VSNR and VIF to test the visible watermarking in order to prove the visual watermarking framework based on HVS. From the experimental results, our proposed technique not only improves the VSNR and VIF 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.