Enhanced Robustness in Image Watermarking using Block Turbo Codes

In this paper, we investigate the improvement achieved by turbo coding for robustness in still image watermarking. We use an error correcting scheme based on the concatenation of a BCH product code and a repetition code. The product code is iteratively decoded using the Chase-Pyndiah algorithm (turbo decoded). For this study, we set the watermarking distortion to around 38 dB and we consider different payloads that can correspond to different applications and services. We compare different coding strategies (i.e. repetition code only and a concatenation of product and repetition codes) in terms of robustness to different photometric attacks, in particular additive noise or lossy compression. Typically, for a payload of 121 bits, the robustness gain for a given message error probability is significant: first error appears at a JPEG quality factor of about 25% with the new coding scheme instead of about 50% when using only repetition codes.