Rotation-Invariant Registration Algorithm of Optical and SAR Images Using Fast Bilateral Filters and Fourier-Based Descriptors

Determining precise main orientations for optical and synthetic aperture radar (SAR) image registration is challenging because of serious radiometric differences and multiplicative speckles. In this letter, a rotation-invariant registration algorithm of optical and SAR images is proposed based on fast bilateral filters and Fourier-based descriptors. First, two nonlinear scale spaces are, respectively, designed for optical and SAR images based on fast bilateral filters to preserve structural features of the images while smoothing. The consistent gradients of the images are calculated in the process using the Sobel operator and the ratio of exponentially weighted average operator, respectively. Then, a novel framework is proposed for rotation-invariant optical and SAR image registration. In the framework, Harris detectors are utilized to detect sufficient and reliable feature points in the scale spaces, and downsampled Fourier-based descriptors, achieving a high discriminability by avoiding the process of orientation assignment, are designed for rotation-invariant and fast feature description. Experiments on three pairs of optical and SAR images demonstrate the effectiveness of the proposed algorithm compared to existing state-of-the-art algorithms.