SYNOPSIS:
    FILTSEP_NLG_ZFROMB axis sigma sigmaw [factor]

DESCRIPTION:
    Do a separated NLG filter on axis. Sigma determines the
    deviation of the gaussian in the spatial domain, sigmaw the
    deviation of the gaussian in the grey value domain.
    Factor can be used to stretch the searched window. It defaults
    to 2*sigma.
    The center pixel for evaluating the deviation in the greyscale
    domain is taken from the backing store.
