Complexity-scalable compensation of geometrical distortions in image watermarking

Geometrical transformations are one of the most important issues to be solved to increase the robustness of digital image watermarking systems. This paper presents an efficient method for inverting geometrical distortions that may spatially desynchronise a watermark detector. We propose a strategy that is scalable in transform complexity, since in some cases a simple transformation is sufficient to compensate the geometrical distortion while in other cases a more complex transform is needed. The strategy is implemented using an orthogonal polynomial mapping, which is efficiently scalable in complexity. To estimate the parameters of the polynomial, we use feature points. The results of the watermark detection after image registration are presented in the form of bit error rate (BER).