An improved retrieval method for amplitude modulation based digital watermarking

In this paper, we propose an improved retrieval method for digital watermarking based on amplitude modulation. Conceptually, the watermark retrieval is achieved from the prediction of a linear combination of neighboring pixel values around a watermarked pixel. By discarding the most different pixel value from eight surrounding pixels, the bias caused by an unequal bit pattern of watermark signal and too much difference in value of neighboring pixels can be reduced. The experimental results show the improved performance of the proposed retrieval method, even if the watermarked images are attacked by various types of digital signal processing i.e. high pass filtering, blurring, and uniform distributed noise adding, compared to previous methods.