Digital Registration Techniques For Sequential Fundus Images

Abstract

Precise registration techniques are essential for quantitative evaluation of sequential fundus images to make early detection of fundus anomalies feasible. The familiar correlation techniques for achieving such image registration are computationally intensive and suffer from non-uniqueness of solution. We have developed an accurate, yet fast, algorithm for image registration by using a combination of power spectrum and power cepstrum analyses. In this new algorithm rotational shifts and translational shifts are corrected separately. The technique involves two main ideas. First, a rotational shift is corrected and changed into a translational shift by computing Fourier power spectrums. After the rotational shift has been corrected, i.e., images are parallel, the remaining translational shifts are handled. Because of the accuracy characteristics of the power cepstrum and the speed of the-FFT, this new algorithm can work very fast and accurately compared to conventional techniques. Also, the cepstrum technique has better tolerance of image noise than the traditional correlation measures. The accuracy obtained and computational time required for the cepstrum-based registration techniques will be illustrated by operating on sequential fundus images used in early detection of glaucoma.