lkblend blends two objects in the specified ratio.
The blending ratio of the objects can be specifed as
a constant or an input object can be used for supplying
the ratios. The constant is used only if the ratio
object is NULL. An optional input object can be used
to specify regions in which the operation is not to be
performed. The value segment of the gating object
is used to determine if the blending on a point is to
be gated.