A new similarity criterion for retinal image registration

Registration methods invariably demand the evaluation of similarity between image areas using criteria based on the maintenance of pixel relative intensities. Because of the severe brightness changes in retinal images, intensity dependent similarity measures are often unable to produce useful registration results. The main purpose of this paper is the presentation of a new similarity evaluation criterion, prepared to overcome the problems raised by important brightness modifications in the images to register. The new criterion is based on the detection of edge point localizations, which are used to assess the correspondence of the compared areas. Some attention was also dedicated to the measure calculation process, and, as an ultimate result, a two-stage implementation was adopted. The values generated by the similarity measure determination step are later used by two registration algorithms prepared to compensate for distinct geometric misalignments between the images