Trellis-coded rational Dither Modulation for digital watermarking

Rational Dither Modulation has been proposed as an effective QIM watermaking algorithm which is robust against value-metric scaling. Invariance is obtained by quantizing a rational function of the host features instead of the features themselves. In this paper we propose a vector extension of the basic RDM scheme. Specifically, a sequence of feature ratios is quantized vectorially with the aid of a properly designed dirty trellis code. A fast sub-optimum embedding algorithm is proposed ensuring fast watermark insertion and good distortion properties. Preliminary results show that a significant advantage is obtained with respect to conventional RDM.