matplotlib-devel Mailing List for matplotlib

I've been using the animations subpackage since it was introduced, but I
only recently tried to save an animation using the `save` method.
Unfortnately, I get a RuntimeError whenever I try to use it:

...
  File
"/Users/Tony/python/devel/mpl/lib/matplotlib/backends/backend_agg.py", line
4
52, in print_raw
    renderer._renderer.write_rgba(filename_or_obj)
RuntimeError: Error writing to file


This can be reproduced with any animation example, e.g.
simple_anim.py<http://matplotlib.sourceforge.net/examples/animation/simple_anim.html>,
by
replacing `plt.show()` with `ani.save('simple_anim.avi')`. The actual error
is from a shell call to ffmpeg, which roughly boils down to:

#~~~~
    import subprocess
    import matplotlib.pyplot as plt

    fig, ax = plt.subplots()
    ax.plot([0, 1])
    command = ['ffmpeg', '-f', 'rawvideo', '-vcodec', 'rawvideo',
               '-s', '800x600', '-pix_fmt', 'rgba', '-r', '5.0',
               '-i', 'pipe:', '-vcodec', 'mpeg4', '-y', 'test.avi']
    proc= subprocess.Popen(command, shell=False, stdout=subprocess.PIPE,
                           stderr=subprocess.STDOUT, stdin=subprocess.PIPE)
    fileobj = proc.stdin
    fig.savefig(fileobj, format='rgba', dpi=100)
#~~~~

(I just copied the ffmpeg command from an example run, so the option values
may vary on other systems.) The error here is the same, and, unfortunately,
not very informative. Is this saving functionality platform dependent? (I'm
on osx.)

Thanks,
-Tony

I've had problems saving MxNx3 (RGB) numpy arrays as images using
imsave. It fails with an exception, and the problem seems to be line
1243 in image.py:

figsize = [x / float(dpi) for x in arr.shape[::-1]]

The purpose of arr.shape[::-1] seems to be to reorder the height and
width dimensions. It works as intended for MxN arrays, but not NxMx3
arrays -- they cause a function to complain about an argument too
many.

I have modified the above line to use (arr.shape[1], arr.shape[0])
instead of arr.shape[::-1], and that solves the problem for me, and I
get the output I expect (and the code still passes all tests it should
pass). However, there could very well be subtleties in the codebase
that I don't know about.

The attached patches add a simple test case, the above mentioned
change and a few updates to the documentation of imsave.

Best,

Jostein.