Old question, lots of good answers, but there might still be interest in another alternative...
The numpngw module that I recently put up on github (https://github.com/WarrenWeckesser/numpngw) can write animated PNG files from numpy arrays. (Update: numpngw is now on pypi: https://pypi.python.org/pypi/numpngw.)
For example, this script:
import numpy as np
import numpngw
img0 = np.zeros((64, 64, 3), dtype=np.uint8)
img0[:32, :32, :] = 255
img1 = np.zeros((64, 64, 3), dtype=np.uint8)
img1[32:, :32, 0] = 255
img2 = np.zeros((64, 64, 3), dtype=np.uint8)
img2[32:, 32:, 1] = 255
img3 = np.zeros((64, 64, 3), dtype=np.uint8)
img3[:32, 32:, 2] = 255
seq = [img0, img1, img2, img3]
for img in seq:
img[16:-16, 16:-16] = 127
img[0, :] = 127
img[-1, :] = 127
img[:, 0] = 127
img[:, -1] = 127
numpngw.write_apng('foo.png', seq, delay=250, use_palette=True)
creates:
You'll need a browser that supports animated PNG (either directly or with a plugin) to see the animation. Firefox does, Safari doesn't, and Chrome has a plugin for it.