Re: [Matplotlib-users] overlaying a plot repeatedly

On Wed, Jul 29, 2009 at 6:09 PM, John Hunter <jd...@gm...> wrote:

> On Wed, Jul 29, 2009 at 6:50 PM, Art<gre...@gm...> wrote:
>
> > My bottleneck now is actually saving the pngs for mencoder to make into
> an
> > avi (as with the movie_demo example on your site) using savefig. Do you
> also
> > know of an alternative way of generating an avi of the animation? My
> > animation has about 9000 frames.
>
> No, I can't imagine there is much fat to trim in that part of the
> code.  We're using libpng to write the png, so no speedups there
> unless you can make the pngs smaller.  It looks like we are using a
> memory pointer to get the rgba data from agg over to png, so no
> speedups there either.  Perhaps Michael has some input.  Some code
> that we could run and test might help produce some further
> optimizations.
>
> JDH
>

Below is some sample code that creates the directory ~/tmp/blit_test,
outputs 50 pngs, and creates a mov.avi using /usr/local/bin/mencoder.
Apologies in advance for the code:

import os
import numpy as np
import matplotlib.pyplot as plt
import subprocess

movdir = os.path.join(os.path.expanduser('~'), 'tmp', 'blit_test')
try: os.mkdirs(movdir)
except: pass
mencoder = '/usr/local/bin/mencoder'

ax = []
im = []
vl = []

fig = plt.figure()

ax.append(fig.add_subplot(2,2,1))
im.append(ax[-1].imshow(np.random.randn(100,100)))
ax[-1].set_xticks([])
ax[-1].set_yticks([])

ax.append(fig.add_subplot(2,2,2))
im.append(ax[-1].imshow(np.random.randn(32,32)))
ax[-1].set_xticks([])
ax[-1].set_yticks([])

ax.append(fig.add_subplot(2, 1, 2))

r = np.abs(np.random.normal(0,0.1,1000))
for i in range(100):
    ras = np.nonzero(np.random.poisson(r))[0]
    ax[-1].scatter(ras, np.ones(len(ras)) * (i+1), s=1, alpha=0.5)

vl.append(ax[-1].axvline(-1, color='r', alpha=0.9, linewidth=2.))
ax[-1].set_xlim([0,1000])
ax[-1].set_ylim([0,100])
plt.draw()

canvas = fig.canvas
background = canvas.copy_from_bbox(fig.bbox)

for i in range(50):
    canvas.restore_region(background)
    im[0].set_data(np.random.randn(100,100))
    ax[0].draw_artist(im[0])

    im[1].set_data(np.random.randn(32,32))
    ax[1].draw_artist(im[1])

    vl[0].set_xdata([i,i])
    ax[2].draw_artist(vl[0])

    canvas.blit()
    plt.savefig(os.path.join(movdir, '%03d' % (i+1)))

fps = 10

command = (mencoder,
           'mf://%s/*.png' % (movdir),
           #'-vf', 'scale=800:-10',
           '-mf', 'fps=%d' % fps,
           '-ovc', 'lavc',
           '-lavcopts', 'vcodec=mpeg4',
           '-o', os.path.join(movdir, 'mov.avi'))
subprocess.check_call(command)

# output in ~/tmp/blit_test/mov.avi