[matplotlib-devel] PATCH: Accept color/alpha in imsave

[Jostein Bø Fløystad]

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.


0001-Add-test-for-color-alpha-handling-in-imsave.patch
Description: Binary data


0002-Fix-imsave-to-accept-a-third-color-alpha-dimension.patch
Description: Binary data
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Re: [matplotlib-devel] Saving animations

[Benjamin Root]

On Sat, Apr 7, 2012 at 1:34 PM, Tony Yu  wrote:

> 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,
>  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
>
>
Tony,

The animation saving feature has be completely rewritten by Ryan recently
and is in master.  Could you give that a try?

Ben Root
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