中文摘要：

为提高数字水印图像对常规信号和复杂几何攻击的抵抗能力,利用SIFT（scale invariant feature transform）特征点的稳健性和交比值不变特性,提出了一种数字图像顽健水印算法。首先,在原图像经过NSCT（nonsubsampled contourlet transform）变换后的低频子带系数中提取SIFT特征点并对其进行优化筛选,从中确定满足“近凸正四边形”的系数区域作为水印嵌入的局部区域,然后利用事先设定好的一些交比值在各局部区域中确定要嵌入水印的具体系数,最后利用奇偶量化调制方法嵌入水印信息。与传统算法相比,在提取水印信息时无需对含水印图像进行几何逆变换。实验结果表明,该算法对常规信号处理及多种几何攻击具有较强的抵抗能力和顽健性。

英文摘要：

In order to improve the robustness of the digital watermarking image against common image processing and complex geometric attacks, a novel robust watermarking scheme of digital image was proposed by using the stable SIFT（scale invariant feature transform） feature points and the cross-ratio values with the characteristic of invariability. Firstly, the original digital image was decomposed with NSCT （non-subsampled contourlet transform）, thus the SIFT feature points were extracted in the NSCT low-frequency coefficients. By optimizing and screening these SIFT feature points, some stable SIFT feature points were gotten and some quadrilateral regions which met the needs of ＂near-convexity square＂ were searched out in these stable feature points. These quadrilateral regions would be used as local watermarking regions. Secondly, some cross-ratio values designed in advance were used to determine the low-frequency coefficients to be embedded watermarking information. Lastly, the watermarking information was em- bedded in these low-frequency coefficients by using odd-even quantization index modulation method. Compared with the traditional algorithms, the image embedded watermarking information and attacked by geometric distortion does not conduct inverse geometric transform when the watermarking information was extracted. Experimental results show that the proposed scheme has a good ability of robustness against common image orocessing and various geometric attacks_