Statistical Image Watermark Decoder using High-order Difference Coefficients and Bounded Generalized Gaussian Mixtures-based HMT

Abstract Imperceptibility, robustness and data payload are three main requirements of any image watermarking systems to guarantee desired functionalities, but there is a tradeoff among them from the information-theoretic perspective. In order to achieve this balance, in this paper, we propose a new statistical image watermarking scheme in nonsubsampled Shearlet transform (NSST) domain, which is based on high-order difference coefficients and bounded generalized Gaussian mixture model (BGGMM) based hidden Markov tree (HMT). In embedding process, NSST is firstly performed on host image and NSST highpass subband is divided into no-overlapping blocks. Then high-order differences of NSST coefficient blocks are computed. And finally, watermark signal is inserted into robust high-order difference coefficients through non-linear multiplicative approach. In extraction phase, robust high-order difference coefficients are firstly modeled by employing BGGMM based HMT, which can capture accurately both marginal distributions and strong dependencies of high-order difference coefficients. Statistical model parameters are then estimated by combining the approach of minimizing the higher bound on data negative log-likelihood function and upward–downward algorithm. And finally, an image watermark decoder is developed using BGGMM based HMT and maximum likelihood decision. Experimental results on some test images and comparison with well-known existing methods demonstrate the efficacy and superiority of the proposed scheme.