A novel multibit watermarking scheme combining spread spectrum and quantization

This paper presents a new multibit watermarking method. The method uses multiple orthonormalized watermark patterns of the same size as the host signal. In particular, the elements of each watermark pattern follow independent normal distribution. Each bit of the transmitted message is hidden using the dither quantizers to modify the projection of the host signal onto its corresponding watermark pattern. As a result, every hidden bit is spread over all elements of the host data and the extracting procedure is blind. Meanwhile, we consider how to choose a suitable quantization step size under the given distortion constraint. It is also proved mathematically that the upper bound of the bit error probability of our method is equal to one of the spread-transform dithered modulation (STDM) under the same situations. Experimental results show our scheme performs better than STDM in terms of bit error probability.