Adaptive angle quantization index modulation for robust image watermarking

A robust image watermarking scheme based on angle quantization index modulation (AQIM) is proposed. The original AQIM method employs a fixed quantization step-size, which results in poor robustness of the algorithm. In this paper, the quantization step-size in AQIM scheme is adaptively selected using an exponential function. To keep the watermark imperceptible and increase its robustness, the low frequency components of high entropy image blocks are used for data hiding. The analytical error probability and embedding distortion are derived and assessed by simulations on artificial signals. Simulation results show that the proposed method has better performance in comparison with the conventional AQIM and recently proposed methods.