This function calculates a similarity measure between two images, after
resampling one into the space of the other. The only supported measure is
currently normalised mutual information, which is also used as a cost
function by the registration algorithms.
The target image. Must have the same dimensionality as the
source image.
targetMask
An optional mask image in target space, whose nonzero
region will be the area over which the measure is calculated.
interpolation
A single integer specifying the type of interpolation
to be applied to the source image when resampling it into the space of the
target image. May be 0 (nearest neighbour), 1 (trilinear) or 3 (cubic
spline). No other values are valid.
Value
A single numeric value representing the similarity between the
images.