基于重同步的高容量鲁棒图像水印算法

如何有效地抵抗组合几何攻击，并且提高水印的嵌入容量，一直是数字水印领域一个具有挑战性的课题.针对此种状况，本文提出了一种抗组合几何攻击，且嵌入容量较大的水印算法.首先利用SURF算法从受攻击的图像提取特征点，并与原图像中的少量鲁棒性较强的特征点匹配，根据特征点对间的坐标关系准确估计出仿射矩阵；然后根据仿射矩阵对失真的图像进行几何校正，恢复水印的重同步.由于几何攻击与还原过程中的像素插值仍会导致变换域水印的位置发生细微的误差，本文在空间域嵌入一层定位水印以便精准地同步；最后，考虑到LT码具有良好的纠删性能，因而先将变换域水印信息进行LT码编码，以尽量提高算法的抗剪切性能.实验结果表明，该算法不仅实现了较高容量的嵌入，而且对于剪切、组合几何攻击具有较好的鲁棒性.

Resynchronization Based High Capacity Robust Image Watermarking Algorithm

How to resist combined geometric attacks effectively and improve the embedded capacity of the watermark has always been a challenging topic in the field of digital watermarking.In view of this situation,a watermarking algorithm that resists combined geometric attacks and has a larger embedded capacity is proposed in this paper.Firstly,feature points from the attacked image are extracted with SURF algorithm,then they are matched with a small amount of feature points of strong robustness,which are extracted from the original image.The matching point pairs are used to estimate the affine matrix accurately and then the geometric attacks are corrected to resynchronize the embedded watermarks.Due to positioning errors introduced during the attacking/correction process,some positioning watermarks are embedded in the spatial domain to improve the accuracy of the resynchronization.Considering the excellent erasure correcting performance of LT codes,the watermark bit sequence is encoded by LT-code such that the anti-cropping performance of the algorithm can be improved.The experimental results show that the proposed algorithm not only has a larger embedding capacity,but also is resistant to the cropping and combined attacks.