Easy animation with matplotlib (mp4, gif)

matplotlib.animation: A handy animation generation library based on matplotlib.

Installation

@mac

$ pip install matplotlib
$ brew install imagemagick #For gif storage
$ brew install ffmpeg #For mp4 storage

matplotlib.Fix rc

$ python -c "import matplotlib;print(matplotlib.matplotlib_fname())"
/Users/riki/.pyenv/versions/ML-2.7.13/lib/python2.7/site-packages/matplotlib/mpl-data/matplotlibrc
$ atom /Users/riki/.pyenv/versions/ML-2.7.13/lib/python2.7/site-packages/matplotlib/mpl-data/matplotlibrc

# line 38
- backend : macosx
+ backend : Tkagg

There are two types of functions that generate Animation

• ArtistAnimation: Prepare all frames in a list in advance
• FuncAnimation: Dynamically generate each frame

Personally, Artist Animation is easier to understand, so I recommend this. FuncAnimation is more flexible, but I don't feel any inconvenience with Artist Animation.

ArtistAnimation

animation.ArtistAnimation(fig, artists, interval=200)

• fig: Outline. matplotlib figure object
• artists: list of list of artist objects (line etc.) drawn in each frame
• interval: Playback interval of each frame [ms]

Note that it is easy to get an error where the artists argument must be a list of list. (Details will be described later)

Example 1: animation of sine wave

anim_sin_wave.py

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation

fig = plt.figure()
x = np.arange(0, 10, 0.1)

ims = []
for a in range(50):
    y = np.sin(x - a)
    line, = plt.plot(x, y, "r")
    ims.append([line])

ani = animation.ArtistAnimation(fig, ims)
ani.save('anim.gif', writer="imagemagick")
ani.save('anim.mp4', writer="ffmpeg")
plt.show()

The pyplot.plot function can plot multiple graphs at once, so the return type is list.

lines = plt.plot(x1, y1, 'r', x2, y2, 'g', x3, y3, 'b')
print type(lines) # list
print len(lines) # 3
print type(lines[0]) # matplotlib.lines.Line2D

For clarity, I dare to unpack the main code to retrieve the Line2D object, then change it to list and then add it to list.

line, = plt.plot(x, y, "r")
ims.append([line])

You can save the animation as follows (anyone who likes gif or mp4)

ani.save('anim.gif', writer="imagemagick")
ani.save('anim.mp4', writer="ffmpeg")

Example 2: Animation of a 2D image

dynamic_image.py

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation

fig = plt.figure()

def f(x, y):
    return np.sin(x) + np.cos(y)

x = np.linspace(0, 2 * np.pi, 120)
y = np.linspace(0, 2 * np.pi, 100).reshape(-1, 1)
ims = []

for i in range(60):
    x += np.pi / 15.
    y += np.pi / 20.
    im = plt.imshow(f(x, y), animated=True)
    ims.append([im])

ani = animation.ArtistAnimation(fig, ims, interval=50, blit=True,
                                repeat_delay=1000)

ani.save('anim.gif', writer="imagemagick")
ani.save('anim.mp4', writer="ffmpeg")
plt.show()

Since the return type of the pyplot.imshow function is an AxesImage object, make it a list and then add it to the list.

im = plt.imshow([[]])
print type(im) # matplotlib.image.AxesImage
ims.append([im])