Make Your Enemy Your Friend: Improving Image Rotation Angle Estimation with Harmonics

It is well known that rotation introduces periodic artifacts into the resulting image. By measuring such periodicities, the rotation angle θ can be estimated from the rotated image without the availability of the original unrotated image. However, existing methods suffer from harmonics, especially when θ is small. This paper revisits the harmonics caused by rotation in the cyclic spectrum and points out that such harmonics can help our rotation angle estimation if used effectively. Based on this observation, we propose aggregating the magnitudes of the candidate peaks and their harmonics in detecting the rotation-specific peak. Both theoretical analyses and experimental results demonstrate the advantage of the proposed scheme over previous methods.