SYNOPSIS:
    FILTSEP_MAX axis size [fromset] [toset]

DESCRIPTION:
    Do a separated maximum filter on axis. Size determines the
    half width ofthe window, fromset contains the classes
    which are considered for maximum determination, toset the
    classes which may be written to.
    Please note, that unexpected results may happen, if a class
    is in toset, but not in fromset. In this case, values may
    _rise_ because the minimum is calculated just from fromset
    voxels, which may be higher than the toset value.
