Fig. 5.

Example of image registration where the gradient information was necessary for successful registration. (a) and (b) WL and AF image pair. The centers of the red circles represent control points. (c) and (d) WL and AF images after preprocessing. (e) Mutual information versus $x$ and $y$ translation at a low resolution. The preliminary translation is indicated by the filled arrow. Note that this translation was not the local maxima with the highest MI (unfilled arrow). It was selected based on its large gradient. Units have been converted from pixels to millimeters. (f) Mutual information versus $x$ and $y$ translation at a high resolution, centered at the preliminary translation. The final translation is indicated by the arrow. Units have been converted from pixels to millimeters. (g) Distance between corresponding control points before (open circles) and after (filled circles) registration, indicating successful registration.