matplotlib动画中出现'格式"rgba"不支持'的问题

Question

我正在尝试用matplotlib制作一个动画，参考了这里的例子。一开始的问题是我的电脑上没有安装ffmpeg，所以我通过macports安装了它，但现在它又说不支持'rgba'。错误信息是：

File "Plot_shocktube1D.py", line 85, in <module>
    animDensity.save(densityAnimationName, extra_args=['-vcodec', 'libx264']) #, writer=movWriter)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/animation.py", line 615, in save
    writer.grab_frame()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/animation.py", line 199, in grab_frame
    dpi=self.dpi)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/figure.py", line 1363, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backend_bases.py", line 2012, in print_figure
    print_method = self._get_print_method(format)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backend_bases.py", line 1953, in _get_print_method
    '%s.' % (format, ', '.join(formats)))
ValueError: Format "rgba" is not supported.
Supported formats: bmp, emf, eps, gif, jpeg, jpg, pdf, pgf, png, ps, raw, rgba, svg, svgz, tif, tiff.

现在，经过一番折腾，我用png替代rgba设置了一个FFMpegWriter，但现在又出现了新的错误...

movWriter = anim.FFMpegWriter(fps=5, codec=None, bitrate=None, extra_args=None, metadata=None)
movWriter.frame_format = 'jpg'
animDensity = anim.FuncAnimation(fig, animateDensity, frames=10, interval=100, blit=True)
animDensity.save(densityAnimationName, extra_args=['-vcodec', 'libx264'], writer=movWriter)

错误信息是：

File "Plot_shocktube1D.py", line 85, in <module>
    animDensity.save(densityAnimationName, extra_args=['-vcodec', 'libx264'], writer=movWriter)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/animation.py", line 615, in save
    writer.grab_frame()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/animation.py", line 199, in grab_frame
    dpi=self.dpi)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/figure.py", line 1363, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backend_bases.py", line 2093, in print_figure
    **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backends/backend_macosx.py", line 326, in print_jpg
    self._print_bitmap(filename, *args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backends/backend_macosx.py", line 319, in _print_bitmap
    self.write_bitmap(filename, width, height, dpi)
ValueError: Unknown file type

我感觉我可能缺少了一些需要安装的东西……通常情况下，macports会帮我安装好所有东西，但我不太确定该去哪里找。任何帮助都将非常感激。

Answer 1

解决办法，我也不知道为什么，就是让matplotlib使用一个叫做“Agg”的东西：

import matplotlib
matplotlib.use("Agg")

Answer 2

那个 use() 的语句对我没什么帮助，但我在尝试让 基本的 matplotlib 动画示例 在 IPython 中运行时，遇到了和你一样的错误。我是通过 macports 安装的 ffmpeg，结果还是收到了那个 rgba 不支持的警告（尽管 rgba 在支持的格式列表中出现了！）。

不过，我发现如果我使用明确的 FFMpegFileWriter（而不是仅仅使用 FFMpegWriter），一切就正常了，rgba 的问题也解决了，我得到了一个可以用的 m4v 文件：

import matplotlib.animation as animation
fig2 = plt.figure()

x = np.arange(-9, 10)
y = np.arange(-9, 10).reshape(-1, 1)
base = np.hypot(x, y)
ims = []
for add in np.arange(15):
    ims.append((plt.pcolor(x, y, base + add, norm=plt.Normalize(0, 30)),))

im_ani = animation.ArtistAnimation(fig2, ims, interval=50, repeat_delay=3000, blit=True)
im_ani.save('im.m4v', writer=animation.FFMpegFileWriter(), metadata={'artist':'Guido'})