On Tue, Aug 24, 2010 at 10:28 PM, David Pine <djp...@gmail.com> wrote:
> I am trying to save the frames from a matplotlib animation and I have a
> question that is undoubtedly based on a profound lack of understanding about
> how matplotlib/python works, but I'm hoping someone can offer me an
> explanation. The following code is excerpted from the animation examples
> "animation_blit_wx.py". The example works fine unless I include the #*****
> line meant to record the animations in included. If the line is included,
> the animated line is no longer drawn to the screen or to the sequence of
> plots I am trying to save. That is, the background is displayed and saved,
> but not the animated line. Why?
>
>
> def update_line(*args):
> global blit_time
>
> if update_line.background is None:
> update_line.background = canvas.copy_from_bbox(ax.bbox)
>
> # restore the clean slate background
> canvas.restore_region(update_line.background)
> # update the data
> line.set_ydata(npy.sin(x+update_line.cnt/10.0))
> # just draw the animated artist
> ax.draw_artist(line)
> # just redraw the axes rectangle
>
> t = time.time()
> canvas.blit(ax.bbox)
> blit_time += time.time() - t
> #***** plt.savefig('f' + str(update_line.cnt) + '.png') *****
>
> if update_line.cnt == NBLITS:
> # print the timing info and quit
> frame_time = time.time() - tstart
> print '%d frames: %.2f seconds' % (NBLITS, frame_time)
> print '%d blits: %.2f seconds' % (NBLITS, blit_time)
> print
> print 'FPS: %.2f' % (NBLITS/frame_time)
> print 'BPS: %.2f' % (NBLITS/blit_time)
> sys.exit()
>
> update_line.cnt += 1
> wx.WakeUpIdle()
>
>
>
Technically speaking, animation to the screen is completely different from
what you are trying to do here. When showing an animation to the screen, a
bunch of tricks are needed to make it efficient and for looping. However,
if you only wish to save the individual frames, I would suggest that you
just simply create your figures normally (none of this blitting and
update_lines stuff) and save each of them as you would normally. Be sure to
call clf() to prevent memory usage to grow out of control.
Persoanlly, I then use ImageMagick to merge the image files together into an
animated gif:
convert `ls -1 *.png | sort -d` -set delay 40 -set dispose none -loop 0
animation.gif
The experimental Animation module will have some preliminary support for
saving animations (that feature isn't cross-platform right now).
Ben Root
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