Animate a transition between two images in GIMP.

gimpgradientanimate.py

# Find our image, and first and last images.
# Gimp GIF export animates from bottom to top, so these are backwards.
foo = gimp.image_list()[0]
start = foo.layers[0]
end = foo.layers[1]


start.visible = False
end.visible = False
# Step - How much we increase opacity each time.
step = 5
for op in xrange(0, 100, step):
    snew = start.copy()
    enew = end.copy()
    print enew.opacity
    snew.opacity = float(op)
    enew.opacity = 100.0 - op
    foo.add_layer(enew, 1)
    foo.add_layer(snew, 2)
    enew.visible = True
    snew.visible = True
    foo.merge_down(enew, EXPAND_AS_NECESSARY)

start.visible = True
end.visible = True