How to animate a time-ordered sequence of matplotlib plots

Question

I want to plot a sequence of .png images in matplotlib. The goal is to plot them rapidly to simulate the effect of a movie, but I have additional reasons for wanting to avoid actually creating an .avi file or saving matplotlib figures and then viewing them in sequence outside of Python.

I'm specifically trying to view the image files in sequence inside a for-loop in Python. Assuming I have imported matplotlib correctly, and I have my own functions 'new_image()' and 'new_rect()', here's some example code that fails to work because of the blocking effect of the show() function's call to the GUI mainloop:

 for index in index_list:
     img = new_image(index)
     rect = new_rect(index)

     plt.imshow(img)
     plt.gca().add_patch(rect)
     plt.show()

     #I also tried pausing briefly and then closing, but this doesn't
     #get executed due to the GUI mainloop from show()
     time.sleep(0.25)
     plt.close()

The above code works to show only the first image, but then the program just hangs and waits for me to manually close the resultant figure window. Once I do close it, the program then just hangs and doesn't re-plot with the new image data. What should I be doing? Also note that I have tried replacing the plt.show() command with a plt.draw() command, and then adding the plt.show() outside of the for-loop. This doesn't display anything and just hangs.

Answer 1

Based on http://matplotlib.sourceforge.net/examples/animation/simple_anim_tkagg.html:

import time
import numpy as np
import matplotlib
matplotlib.use('TkAgg') # do this before importing pylab

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111)

def animate():
    tstart = time.time()                   # for profiling
    data=np.random.randn(10,10)
    im=plt.imshow(data)

    for i in np.arange(1,200):
        data=np.random.randn(10,10)
        im.set_data(data)
        fig.canvas.draw()                         # redraw the canvas
    print 'FPS:' , 200/(time.time()-tstart)

win = fig.canvas.manager.window
fig.canvas.manager.window.after(100, animate)
plt.show()

---

plt.imshow can accept a float array, uint8 array, or a PIL image. So if you have a directory of PNG files, you could open them as PIL images and animate them like this:

import matplotlib
matplotlib.use('TkAgg') # do this before importing pylab
import matplotlib.pyplot as plt
import Image
import glob

fig = plt.figure()
ax = fig.add_subplot(111)

def animate():
    filenames=sorted(glob.glob('*.png'))
    im=plt.imshow(Image.open(filenames[0]))
    for filename in filenames[1:]:
        image=Image.open(filename)
        im.set_data(image)
        fig.canvas.draw() 

win = fig.canvas.manager.window
fig.canvas.manager.window.after(100, animate)
plt.show()