（1 中國傳媒大學 信息工程學院，北京 100024
2 中國傳媒大學 計算機學院，北京 100024
3 中國傳媒大學 廣播電視數字化教育部工程中心，北京 100024）
摘要
　　　為保證數字圖像水印的魯棒性和不可見性，本文提出了一種基于DCT域DC系數二次變換的水印嵌入算法。該算法首先將原始載體圖像進行一次分塊DCT變換，提取一次DCT變換后的DC系數,將其生成新矩陣后進行二次DCT變換，通過多種實驗結果比較，選擇將水印嵌入到DC系數二次變換后的高頻系數上，并在此基礎上，結合人眼視覺系統（HVS）的亮度掩蔽特性以及不同的塊可嵌入的水印容量的不同，通過計算二次DC系數矩陣每個分塊的方差，自適應選擇可嵌入水印的DCT塊。該算法不僅具有較好的不可感知性，而且對諸如JPEG壓縮、旋轉、幾何剪切、疊加噪聲等攻擊均具有較好的魯棒性，且能保證含有水印的圖像的質量。
　　　 
關鍵詞
　　數字圖像水印 DCT變換 直流系數(DC) 二次變換
Abstract
　　Considering the robustness and imperceptibility of digital image watermarking, this paper proposes an watermark embedding algorithm, in which watermark is embedded in DC coefficients derived from a dual DCT transformations. After block based DCT transformation, DC coefficients of an image are arranged into a new matrix, on which block based DCT transformation is performed again. Through abound empirical tests, high frequency coefficients of DCT transformation are selected to be embedded with watermark. Allowing for properties of the human visual system (HVS), variance of each block is calculated to determine whether a bit will be embedded into it. Simulation tests demonstrate that the algorithm not only has good imperceptibility, but also has good robustness for JPEG compression, rotation, geometric shear, imposed noise and other attacks, etc.

Keywords—digital image watermarking; DCT transformation; DC coefficients; dual transformation

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作者簡介：
王秀麗  目前就讀于中國傳媒大學信息工程學院，主修通信與信息系統專業。