scipy: savefig without frames, axes, only content

EDIT

Changed aspect='normal to aspect='auto' since that changed in more recent versions of matplotlib (thanks to @Luke19).

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Assuming :

import matplotlib.pyplot as plt

To make a figure without the frame :

fig = plt.figure(frameon=False)
fig.set_size_inches(w,h)

To make the content fill the whole figure

ax = plt.Axes(fig, [0., 0., 1., 1.])
ax.set_axis_off()
fig.add_axes(ax)

Then draw your image on it :

ax.imshow(your_image, aspect='auto')
fig.savefig(fname, dpi)

The aspect parameter changes the pixel size to make sure they fill the figure size specified in fig.set_size_inches(…). To get a feel of how to play with this sort of things, read through matplotlib's documentation, particularly on the subject of Axes, Axis and Artist.

You can find the bbox of the image inside the axis (using get_window_extent), and use the bbox_inches parameter to save only that portion of the image:

import numpy as np
import matplotlib.pyplot as plt

data=np.arange(9).reshape((3,3))
fig=plt.figure()
ax=fig.add_subplot(1,1,1)
plt.axis('off')
plt.imshow(data)

extent = ax.get_window_extent().transformed(fig.dpi_scale_trans.inverted())
plt.savefig('/tmp/test.png', bbox_inches=extent)

I learned this trick from Joe Kington here.

An easier solution seems to be:

fig.savefig('out.png', bbox_inches='tight', pad_inches=0)