数字水印的鲁棒性评测模型

数字水印的鲁棒性是水印技术实用化的一个重要指标.与通过StirMark测试和各种仿真测试不同,定义互信息作为代价函数,建立水印系统鲁棒性描述和度量的一般模型.以扩频水印和量化水印为范例,推导出评测鲁棒性的互信息度量计算模型,并仿真分析了高斯噪声和JPEG压缩条件下互信息函数对鲁棒性的评估结果.实验以统计误比特率的方法计算图像DCT域中低频系数为载体的扩频水印误码率和一段音频数据三级小波细节系数为载体的量化水印误码率.互信息函数和误码率之间的匹配关系验证了互信息度量模型的有效性,互信息函数可以作为代价函数预测误码率的变化趋势.关键词：数字水印鲁棒性互信息误码率

Evaluation model for robustness of digital watermarking

Robustness is one of the most important requirements when digital watermarking is applied. Different from the StirMark test and various simulation tests, a mutual information function is defined as a criterion to measure the robustness of watermarking algorithm. Taking the additive spread spectrum watermarking scheme and quantization index modulation (QIM) watermarking scheme as two examples, the calculation formulas of mutual information function are derived to evaluate the robustness of the algorithms. Numerical computation of mutual information is performed with change of watermark noise rate (WNR). In the experiment, spread spectrum watermarking is implemented in discrete cosine transform (DCT) and QIM watermarking is implemented in discrete wavelet transform (DWT). The statistic bit error rate (BER) is derived against Gaussian distribution noise and JPEG compression. Experiment results show that the evaluation conclusion of mutual information method is in accordance with the empirical BER. Mutual information can be selected as a cost function to predict the BER.