如何保存 matplotlib 动画的最后一张图片？

Question

我想知道如何在 Python 3 中保存FuncAnimation的最后一张图像。这是一些代码：

import matplotlib.animation
from mpl_toolkits.mplot3d import Axes3D

ani = matplotlib.animation.FuncAnimation(fig, _update_2d_graph, frames=9, interval=600, repeat_delay=5000, blit=False)
ani.save(output_dir, writer="imagemagick")

其中_update_2d_graph是一个函数，根据帧数提供不同的点偏移：

def _update_2d_graph(num):
    x_updated = np.hstack((pos_gt.x[:num].tolist(),pos_pred.x[:num].tolist()))
    y_updated = np.hstack((pos_gt.y[:num].tolist(),pos_pred.y[:num].tolist()))

    paths_gt = []
    paths_ped = []

    for i in range(num):
        marker_gt = mmarkers.MarkerStyle('o')
        marker_ped = mmarkers.MarkerStyle('x')
        path_gt = marker_gt.get_path().transformed(marker_gt.get_transform())
        path_ped = marker_ped.get_path().transformed(marker_ped.get_transform())
        paths_gt.append(path_gt)
        paths_ped.append(path_ped)

    graph._paths = np.concatenate([paths_gt, paths_ped])
    graph.set_facecolors(np.concatenate([colors[:num], colors[:num]]))
    graph.set_edgecolors(np.concatenate([colors[:num], colors[:num]]))
    graph.set_offsets(np.hstack((y_updated[:, np.newaxis], x_updated[:, np.newaxis])))

而不是保存整个动画（例如作为 .gif 文件），我想保存动画的最后一个时间步的 .png。 是否可以访问动画对象中的最后一帧？

我不想调用_update_2d_graph(9)因为这个调用已经被动画对象执行了，我也不想通过另一个FuncAnimation调用重新迭代整个 9 帧。

Answer 1

实际上，我最初的测试表明，在运行动画后保存图形确实会保存最后一帧的状态。 你能测试它以确认吗？

ani = matplotlib.animation.FuncAnimation(fig, _update_2d_graph, frames=9, interval=600, repeat_delay=5000, blit=False)
ani.save(output_dir, writer="imagemagick")
fig.savefig('last_frame.png')

我使用了动画 3D 随机游走示例中的代码：

import numpy as np
import matplotlib.pyplot as plt
import mpl_toolkits.mplot3d.axes3d as p3
import matplotlib.animation as animation

# Fixing random state for reproducibility
np.random.seed(19680801)


def Gen_RandLine(length, dims=2):
    """
    Create a line using a random walk algorithm

    length is the number of points for the line.
    dims is the number of dimensions the line has.
    """
    lineData = np.empty((dims, length))
    lineData[:, 0] = np.random.rand(dims)
    for index in range(1, length):
        # scaling the random numbers by 0.1 so
        # movement is small compared to position.
        # subtraction by 0.5 is to change the range to [-0.5, 0.5]
        # to allow a line to move backwards.
        step = ((np.random.rand(dims) - 0.5) * 0.1)
        lineData[:, index] = lineData[:, index - 1] + step

    return lineData


def update_lines(num, dataLines, lines):
    for line, data in zip(lines, dataLines):
        # NOTE: there is no .set_data() for 3 dim data...
        line.set_data(data[0:2, :num])
        line.set_3d_properties(data[2, :num])
    return lines

# Attaching 3D axis to the figure
fig = plt.figure()
ax = p3.Axes3D(fig)

# Fifty lines of random 3-D lines
data = [Gen_RandLine(25, 3) for index in range(50)]

# Creating fifty line objects.
# NOTE: Can't pass empty arrays into 3d version of plot()
lines = [ax.plot(dat[0, 0:1], dat[1, 0:1], dat[2, 0:1])[0] for dat in data]

# Setting the axes properties
ax.set_xlim3d([0.0, 1.0])
ax.set_xlabel('X')

ax.set_ylim3d([0.0, 1.0])
ax.set_ylabel('Y')

ax.set_zlim3d([0.0, 1.0])
ax.set_zlabel('Z')

ax.set_title('3D Test')

# Creating the Animation object
line_ani = animation.FuncAnimation(fig, update_lines, 25, fargs=(data, lines),
                                   interval=50, blit=False, repeat=True)

### HERE ARE THE ONLY LINES I ADDED ####
line_ani.save('./test.gif', writer='imagemagick')
fig.savefig('./test.png') 

文件test.gif

文件test.png