Pairwise retinal image registration by radial distortion correction

We describe a new method for pairwise retinal image registration. The proposed method is unique in that the radial distortion due to image acquisition is corrected prior to the geometric transformation. Since the overlapping region is typically small in a retinal image pair, only a few correspondences are available, thus limiting the applicable model to an affine transform at best. To recover the distortion due to curved-surface of retina and lens optics, a combined approach of an affine model with a radial distortion correction is proposed. Experimental results confirmed that the affine model with distortion correction could register retinal image pairs to within 1.88±0.35 pixels accuracy assessed by vessel line error, which is 17% better than the affine-only approach. Because the proposed method needs only two correspondences, it can be applied to obtain good registration accuracy even in the case of small overlap between retinal image pairs.