Bias minimizing filter design for gradient-based image registration

Gradient-based image registration techniques represent a very popular class of approaches to registering pairs or sets of images. As the name suggests, these methods rely on image gradients to perform the task of registration. Very often, little attention is paid to the filters used to estimate image gradients. In this paper, we explore the relationship between such gradient filters and their effect on overall estimation performance in registering translated images. We propose a methodology for designing filters based on image content that minimize the estimator bias inherent to gradient-based image registration. We show that minimizing such bias improves the overall estimator performance in terms of mean square error (MSE) for high signal-to-noise ratio (SNR) scenarios. Finally, we propose a technique for designing such optimal gradient filters in the context of iterative multiscale image registration and verify their further improved performance.