Bug summary

Matplotlib is no longer able to create gifs with a transparent background.

Code for reproduction

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

fig, ax = plt.subplots()
xdata, ydata = [], []
ln, = ax.plot([], [], 'ro')

def init():
    ax.set_xlim(0, 2*np.pi)
    ax.set_ylim(-1, 1)
    return ln,

def update(frame):
    xdata.append(frame)
    ydata.append(np.sin(frame))
    ln.set_data(xdata, ydata)
    return ln,

ani = FuncAnimation(fig, update, frames=np.linspace(0, 2*np.pi, 128),
                    init_func=init, blit=True)


savefig_kwargs = {
    "facecolor": "none",
}
ani.save("test.gif", savefig_kwargs=savefig_kwargs)

Actual outcome

With Matplotlib version 3.8.0 (and also 3.7.3) installed this is the ouput:

A gif-file with a white background

Expected outcome

In 3.6.3 and before the file had a transparent background

Additional information

I tried many different setups, different values for facecolor (e.g. (1,1,1,1)), set "transparent": True and googeling quite a lot - old solutions on github won't work.

Like in the expected outcome stated, this worked in the past (until Matplotlib 3.6.3).

There either seems to be an error in the fix for another issue in #21831 - or this is now the new correct behavior, but it seems like the transparency should still work for gifs, as this was an issue with different formats.

Operating system

Windows 11

Matplotlib Version

3.8.0

Matplotlib Backend

TkAgg

Python version

Python 3.12.0

Jupyter version

No response

Installation

pip