A pyramid approach to sub-pixel image fusion based on mutual information

We investigate aspects of multi-modal image registration based on a new criterion named mutual information (or sometimes Shannon information). This criterion is intensity-based and requires no landmarks; hence, its application can be automated without resorting to segmentation. We present a form amenable to derivation with respect to the geometric transformation parameters (here: affine transformation). This form involves Parzen windows; we explore the dependence of the registration accuracy on these windows and propose that they be tuned to each resolution level in a pyramid approach. We conduct experiments and show that both the window width and the number of windows is relevant. In addition, we show that it is beneficial to use a spline-based high-order interpolation scheme for applying the geometric transformation.