Briassouli Alexia, Strintzis Michael G
Department of Electrical and Computer Engineering, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
IEEE Trans Image Process. 2004 Dec;13(12):1604-17. doi: 10.1109/tip.2004.837516.
The issue of copyright protection of digital multimedia data has attracted a lot of attention during the last decade. An efficient copyright protection method that has been gaining popularity is watermarking, i.e., the embedding of a signature in a digital document that can be detected only by its rightful owner. Watermarks are usually blindly detected using correlating structures, which would be optimal in the case of Gaussian data. However, in the case of DCT-domain image watermarking, the data is more heavy-tailed and the correlator is clearly suboptimal. Nonlinear receivers have been shown to be particularly well suited for the detection of weak signals in heavy-tailed noise, as they are locally optimal. This motivates the use of the Gaussian-tailed zero-memory nonlinearity, as well as the locally optimal Cauchy nonlinearity for the detection of watermarks in DCT transformed images. We analyze the performance of these schemes theoretically and compare it to that of the traditionally used Gaussian correlator, but also to the recently proposed generalized Gaussian detector, which outperforms the correlator. The theoretical analysis and the actual performance of these systems is assessed through experiments, which verify the theoretical analysis and also justify the use of nonlinear structures for watermark detection. The performance of the correlator and the nonlinear detectors in the presence of quantization is also analyzed, using results from dither theory, and also verified experimentally.
在过去十年中，数字多媒体数据的版权保护问题备受关注。一种日益流行的有效版权保护方法是水印技术，即在数字文档中嵌入仅能由其合法所有者检测到的签名。水印通常使用相关结构进行盲检测，在高斯数据的情况下这将是最优的。然而，在离散余弦变换（DCT）域图像水印的情况下，数据的尾部更重，相关器显然不是最优的。非线性接收器已被证明特别适合在重尾噪声中检测微弱信号，因为它们在局部是最优的。这促使使用高斯尾部零记忆非线性以及局部最优的柯西非线性来检测DCT变换图像中的水印。我们从理论上分析了这些方案的性能，并将其与传统使用的高斯相关器的性能进行比较，同时也与最近提出的广义高斯检测器进行比较，后者的性能优于相关器。通过实验评估了这些系统的理论分析和实际性能，实验验证了理论分析，并证明了使用非线性结构进行水印检测的合理性。还利用抖动理论的结果分析了相关器和非线性检测器在存在量化情况下的性能，并通过实验进行了验证。
