[Insight-users] Filtering with a mask?

[Atwood, Robert C]

Is there an existing method for smoothing the image only in specified
regions, while leaving other regions untouched? Or,smoothing voxels with
a value less than a trheshold, ignoring contributions from neighbours
that lie outside the threshold?=20

ie. for a simple average smoothing, the new value equals the average of
all values in the neighbourhood which have a value not equal to a
specified value?=20