def __init__(self, zero_layer=None, zero_weight=None):
"""*zero_layer* is the 0 to use in summing up the layers (the start
value), it defaults to 0.
*zero_weight* is the 0 to use in summing up the weights, it default to
0, too."""
if zero_layer is None:
zero_layer = 0
if zero_weight is None:
zero_weight = 0
Stack.__init__(self)
self.zero_layer = asfunction(zero_layer)
self.zero_weight = asfunction(zero_weight)
def __init__(self, background):
Stack.__init__(self)
self.background = asfunction(background)
def __init__(self, background):
"""The *background* yields the background layer, no alpha."""
Stack.__init__(self)
self.background = asfunction(background)
