Analyses of error correction strategies for typical communication channels in watermarking

Most watermarking techniques rely on redundancy where signature bits are encoded in a su$ciently large amount of sites for robustness against distortions and attacks while the watermark energy is kept low enough to remain imperceptible. The goal of this paper is to explore some strategies for exploiting this redundancy using error correcting codes. In some watermarking techniques bits are extracted via hard-decisions leading to a binary symmetric channel model while in others the extraction is carried out with soft-decisions leading to a additive Gaussian channel model. First, we consider error correcting codes for very high error rates of the watermarking channel where the trade-o!s of Bose}Chaudury}Hocquenheim (BCH) and repetition codes are investigated. We also present the performance and a fast implementation of soft-decoders. We give two potential realizations of soft-decoding, namely, Viterbi decoder for convolutional codes and a new algorithm for soft-BCH decoding. 2001 Elsevier Science B.V. All rights reserved.