Robust estimation of amplitude modification for scalar Costa scheme based audio watermark detection

Abstract

Recently, informed watermarking schemes based on Costa's dirty paper coding are drawing more attention than spread spectrum based techniques because these kinds of watermarking algorithms do not need an original host signal for watermark detection and the host signal does not affect the performance of watermark detection. For practical implementation, they mostly use uniform scalar quantizers, which are very vulnerable against amplitude modification. Hence, it is necessary to estimate the amplitude modification, i.e., a modified quantization step size, before watermark detection. In this paper, we propose a robust algorithm to estimate the modified quantization step size with an optimal search interval. It searches the quantization step size to minimize the quantization error of the received audio signal. It does not encroach the space for embedding watermark message because it just uses the received signal itself for estimation of the quantization step size. The optimal searching interval is determined to satisfy both detection performance and computational complexity. Experimental results show that the proposed algorithm can estimate the modified quantization step size accurately under amplitude modification attacks. © Springer-Verlag Berlin Heidelberg 2005.