RST-invariant digital image watermarking based on log-polar mapping and phase correlation

Based on log-polar mapping and phase correlation, this paper presents a novel digital image watermarking scheme that is invariant to rotation, scaling, and translation (RST). We embed watermark in the log-polar mappings of Fourier magnitude spectrum of original image, and use the phase correlation between the LPM of the original image and the LPM of the watermarked image to calculate the displacement of watermark positions in LPM domain. The scheme preserves the image quality by avoiding computing inverse log-polar mapping (ILPM), and produces smaller correlation coefficient for unwatermarked images by using phase correlation to avoid exhaustive search. The evaluations demonstrate that the scheme is invariant to rotation and translation, invariant to scaling when the scale is in a reasonable range, and very robust to JPEG compression. Keywords— digital image watermarking RST invariant Fourier-Mellin Transform LPM ILPM cross-power spectrum phase correlation