Changing alpha channel of image in pylab


Changing the alpha-channel of a plotted image doesn't work for me in an ipython (pylab) shell.

The example below illustrates the problem (i hope so at least ...)
Running it with %run - everything is fine and the two images look the same.

Runing it line by line without the show, the figure shows up, the images are plotted, but the alpha-value of im1 is not set correctly so it's fully opaque in the left plot.

Is it just me or is it a bug, and if it's a bug is it a bug in pylab or in matplotlib?

Thanks in advance!


import numpy as np
from matplotlib.pyplot import *

aimg = np.array([[0, 1, 1, 0],
                  [0, 1, 2, 0],
                  [0, 1, 3, 0],
                  [0, 1, 4, 0]])

ax = subplot(121)
im1 = imshow(aimg, alpha = 1, interpolation='nearest')

ax = subplot(122)
im2 = imshow(aimg, alpha = 0.5, interpolation='nearest')