PHASE INFORMATION IN RST INVARIANT IMAGE WATERMARKING
Yao Jianping · Proceedings of the CSEE · 2005
We anticipate extensive applications of digital watermarking in the future electric power systems, which can be copyright protection, content authentication, quality measurement, database indexing and retrieval, etc. In this paper, we present a new digital image watermarking scheme that is invariant to rotation, scaling, and translation (RST). We embed watermark in the log-polar mappings (LPM) of the Fourier amplitude spectrum of an original image, so that image scaling results in a translational shift along the log-radius axis, that image rotation results in a cyclical shift along the angle axis, and that image translation has no effects in the LPM domain. In order to invert the translation effect in the LPM domain of image rotation and scaling, we propose our filtering method, which is new to our best knowledge. The new filtering method uses a small portion of the LPM spectrum of the original image to calculate the translated watermark positions. With minimum cost, the nearly-blind watermarking scheme avoids exhaustive search to save computation time and reduce false detection. The evaluations demonstrate that the performance of the scheme is very satisfactory.