[Matplotlib-users] Alpha not working from imshow?

[Tim B. <tim...@ma...>]

I'm generating images that I want to use as overlays in Google Earth. Thus, I would like the masked portion of the numpy arrays I am using to appear as transparent.
However, I seem to consistently get white instead of a transparent point.

To clarify the issue, I wrote this short piece of code. I am setting both the figure background to transaprent and the masked value to transparent but I get white.

I have pulled the current svn code and built matplotlib. I get the same issue. 

from numpy import ma
import matplotlib.pyplot as plt
from pylab import colorbar, imshow, show, cm


def main():
  a = ma.array([[1,2,3],[4,5,6]],mask=[[0,0,1],[0,0,0]])
  fig = plt.figure()
  fig.patch.set_alpha(0.0)
  cmap = cm.jet
  cmap.set_bad(alpha=0.0)
  imshow(a, interpolation='nearest', cmap=cmap)
  colorbar()
  show()

Any thoughts?

Tim B