数字水印信道中的分组码编码策略分析

稳健性是数字水印的重要指标之一.为了改善水印稳健性,一些学者在水印算法中引入了纠错编码(error correcting coding,简称ECC),试图通过纠正水印误码来降低检测误码率.然而,水印信道与一般的通信信道不同,受水印不可察觉性的限制,纠错编码中引入的信息冗余将导致水印嵌入强度的降低.换言之,纠错码的码率会极大地影响到嵌入信号的幅度.由此将引出一个问题:从改善水印稳健性的角度出发,纠错编码的码率应该如何选择?从分析和实验两个方面探讨了这个问题.给出了P1otkin限和Hamming限情况下,水印中的Q进制线性分组码应该满足的码率约束条件,并通过仿真实验检验了给出的条件.

Analysis of Block Coding Strategies in Watermarking Channel

Robustness is one of the important requirements of digital watermark. To improve the robustness of watermarks, some algorithms proposed to apply error correcting coding (ECC) in watermarking, intending to lower the detection error rate by correcting some errors. However, there is an important difference between the watermarking channel and the conventional communication channel. Owing to the constraints of imperceptibility, the redundancy introduced by ECC will result in a decrease of embedding strength for watermarking. In other words, the coding rate of ECC affects the amplitude of embedding signal. Hence, a question arises: For improving watermark robustness, how to choose the coding rate of ECC? In this paper, this problem is addressed both analytically and experimentally. By employing Plotkin Bound and Hamming Bound, the coding rate constraints of Q-symbol linear block codes are derived. The conclusions are demonstrated by the experiment results.