SYNOPSIS:
    FILTB_NLC2 sx sy sz sw [fx] [fy] [fz] [fw]

DESCRIPTION:
    Do a nonlinear gaussian filtering, where the coupling is stored
    as a result into the backbuffer (B). fw is used to scale the
    coupling. Fully coupling areas (single grey value) should get
    FW in the result.
    This differs from FILTB_NLC by using exp(-0.5*|x/sigmaw|)
    for the weighting in w direction.

SEE ALSO:
    FILTB_NLC, FILTB_NLG, FILTB_NLD, NLGS,
    backingstore, COPY_BACKTOGREY, XCHG_GREYANDBACK, ERASE_BACK
