DWT域抗几何攻击水印算法研究

Image Watermarking Scheme in Wavelet Domain against Geometrical Attacks

鲁棒水印面临的最大问题就是几何攻击。小波变换域不具有几何不变性,一个微弱不可察觉的几何攻击就能使小波域水印算法失效。提出了一种新的以特征点作为模板、有效抵抗几何攻击的图像水印算法。它包括:(1)根据小波变换空间各子带呈树形结构的特性,选择每棵小波树中纹理最强的方向子树的树根作为水印嵌入点;(2)根据嵌入点在低频对应位置的能量和该方向子树高频叶子结点的纹理信息确定一种自适应嵌入水印策略;(3)利用Har-ris-Laplace算子从含有水印的图像中提取出具有几何形变鲁棒性的特征点,将其作为模板;(4)水印检测时,先利用特征点模板通过线性变换恢复几何形变的图像,然后通过统计图像的相关性来验证水印的存在,无需原始图像。仿真实验表明,所提出的水印算法不仅具有很好的透明性,而且对常见的图像处理和几何变换具有很好的鲁棒性。

The toughest challenge facing the robust watermarking is the geometrical attacks. A slight even intangible geometrical attack can fail the watermark in wavelet domain due to the shift-variance of wavelet. Based on the feature points, this paper proposed an image watermarking scheme against the geometrical attacks. First, according to the tree structure of the wavelet coefficients, the proposed scheme selected the root of the directional subtree with the highest texture as the embedded points from each wavelet tree. Second, this paper proposed an adaptive embedding strategy according to the energy of the low frequency coefficient corresponding to the embedded point and the texture characteristics of the highest frequency coefficients of the subtree. Finally, the proposed scheme used the Harris-Laplace operator to extract the feature points robust to the geometrical attacks, and form a template of feature points. During detection, the proposed scheme restored the attacked image by linear transformation using the feature template, and then verified the watermarking through statistical correlation. The detection process does not need the original host image. Experi- mental results show that the proposed algorithm has good transparency and is very robust to common image processing and geometric attacks.