中文摘要：

提出了一种基于改良扩频技术的Contourlet盲图像水印算法。将二值水印图像经Arnold置乱后进行双极性映射,然后通过IMSS（Improved Modified Spread Spectrum）系统嵌入到宿主图像Contourlet域次高阶方向子带中能量最大的子带纹理最丰富的位置上,检测端采用相关检测并设置一最佳阈值来判决水印存在与否。实验结果表明该方案不仅具有很好的透明性,而且在常规的图像处理和攻击下比传统扩频水印有更强的鲁棒性,同时也克服了传统扩频水印在检测无水印图像时完全失败的缺点。

英文摘要：

A blind image watermarking algorithm in contourlet domain based on improved modified spread spectrum（IMSS） technique is proposed.The original binary watermark is firstly scrambled by two-dimensional Arnold transform and mapped from unipolarity to bipolarity,and then embedded into the richest textured region of the subband,which has the maximum energy among the second biggest directional subbands of the host image decomposed by the contourlet transform.Meanwhile,the IMSS technique is adopted in the process of watermark embedding.The watermark embedded is retrieved by computing the correlation between the watermarked coefficients and the pseudo random sequences.The optimal threshold is calculated to determine the existence of the watermark in the correlation detector.Experimental results demonstrate that the proposed algorithm not only has good imperceptibility but also has higher robustness against common image processing and attacks than conventional SS（spread spectrum） watermarking;furthermore,it overcomes the major disadvantage of conventional SS watermarking which completely fails if the tested image is pure.