[Matplotlib-users] Leftmost column of PNG output is transparent

Hi All,

I'm trying to plot evenly grided data to tiles for google maps overlays.
Each tile needs to be a 256x256 pixel PNG image, without any borders.

The problem that I'm having is that the leftmost column of the resultant PNG
image (saved using FigureCanvasAgg.print_figure) is transparent.

My real code uses basemap because the output has to be in the mercator
projection, but the sample code below is simplified to exclude it. You can
view the sample image that is produced at this address:
http://earth.usc.edu/ftp/kmilner/trans_test.png

Any ideas?

Thanks!
Kevin

#!/usr/bin/env python

from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure
import numpy

dpi = 64
pixels = 256
fig = Figure(linewidth=0, frameon=False)
canvas = FigureCanvas(fig)

fig.figurePatch.set_alpha(0.0)

ax_bounds = [0, 0, 1, 1]

ax = fig.add_axes(ax_bounds, axisbg=(1.0,1.0,0.0,0.0),
						frameon=False )

inches = pixels / dpi
fig.set_size_inches(256 / dpi, 256 / dpi)

num = 31

z = numpy.empty( (num, num) )

for x in xrange(num):
	for y in xrange(num):
		z[x, y] = x * y

x, y = numpy.meshgrid( range(num), range(num) )

image = ax.pcolor(x, y, z)
image = ax.contourf(x, y, z)

canvas.print_figure("/tmp/trans_test.png", dpi=dpi)
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