Novel angle quantization index modulation scheme for image watermarking

In this paper, we propose a new angle quantization index modulation (AQIM) method, called the difference AQIM (DAQIM) method. The proposed method aims to improve the watermarking performance against gain attacks. Unlike the original AQIM method [1], the DAQIM method quantizes the difference of the two angles instead of the angles themselves. The experimental results demonstrate that our proposed method outperforms both the AQIM and the gradient direction watermarking (GDWM) [2] methods in terms of document-to-watermark ratio (DWR).