Python通过matplotlib包和gif包生成gif动画

时间:2022-10-17 11:16:44

使用​​matplotlib​​​生成gif动画的方法有很多,一般常规使用​​matplotlib​​​的​​animation​​​模块的​​FuncAnimation​​​函数实现。在​​matplotlib​​​官网看到了第三方动画包​​gif​​的介绍。

​gif​​包概述

​gif​​包是支持 ​​Altair​​, ​​matplotlib​​和​​Plotly​​的动画扩展。
​gif​​依赖​​PIL​​,即​​pillow​​,要求​​Pillow>=7.1.2​​。
安装​​gif​​包,​​pip install gif​

动画原理

所有​​动画​​都是由​​帧(frame)​​构成的,一帧就是一幅静止的画面,连续的帧就形成动画。我们通常说帧数,简单地说,就是在1秒钟时间里传输的图片的帧数,也可以理解为图形处理器每秒钟能够刷新几次,通常用​​fps(Frames Per Second)​​表示。制作动画的关键:如何生成帧,每秒多少帧。

​gif​​包解读

​gif​​包非常简洁,只有一个单独的文件​​gif.py​​,文件主要包含​​options​​类、​​frames​​和​​save​​两个函数。

​options​​类

提供精简版 的​​Altair​​, ​​matplotlib​​和​​Plotly​​的保存或输出设置。以​​matplotlib​​为例,提供以下设置。

  • dpi (int): The resolution in dots per inch
  • facecolor (colorspec): The facecolor of the figure
  • edgecolor (colorspec): The edgecolor of the figure
  • transparent (bool): If True, the axes patches will all be transparent

设置方法:​​gif.options.matplotlib["dpi"] = 300​​原理:options在构造函数中创建matplotlib字典保存配置,随后传递给底层的matplotlib包。

​frames​​函数

装饰器函数,通过对应包编写自定义绘图函数生成单帧图像。

​save​​函数

根据帧序列生成动画。

def save(frames, path, duration=100, unit="milliseconds", between="frames", loop=True):
"""Save decorated frames to an animated gif.
- frames (list): collection of frames built with the gif.frame decorator
- path (str): filename with relative/absolute path
- duration (int/float): time (with reference to unit and between)
- unit {"ms" or "milliseconds", "s" or "seconds"}: time unit value
- between {"frames", "startend"}: duration between "frames" or the entire gif ("startend")
- loop (bool): infinitely loop the animation

​frames​即根据​@gif.frame​装饰的绘图函数生成的帧的序列,此处根据需要自定义。
​​​duration​即持续时间,由单位​unit​和模式​between​决定,默认为frames​为帧间的时间间隔
​​​unit​即持续时间单位,支持毫秒和秒,默认为毫秒。
​​​between​即持续时间计算模式,默认​frames​​duration​为帧之间的时间间隔,​startend​模式时​duration=duration /len(frames)​,即​duration​为所有帧—整个动画的持续时间。

​gif​​包生成gif动画实践


import random
from matplotlib import pyplot as plt
import gif

# 构造数据
x = [random.randint(0, 100) for _ in range(100)]
y = [random.randint(0, 100) for _ in range(100)]
# 设置选项
gif.options.matplotlib["dpi"] = 300


# 使用gif.frame装饰器构造绘图函数,即如何生成静态的帧
@gif.frame
def plot(i):
xi = x[i * 10:(i + 1) * 10]
yi = y[i * 10:(i + 1) * 10]
plt.scatter(xi, yi)
plt.xlim((0, 100))
plt.ylim((0, 100))


# 构造帧序列frames,即把生成动画的所有帧按顺序放在列表中
frames = []
for i in range(10):
frame = plot(i)
frames.append(frame)
# 根据帧序列frames,动画持续时间duration,生成gif动画
gif.save(frames, 'example.gif', duration=3.5, unit="s", between="startend")

Python通过matplotlib包和gif包生成gif动画

以心形曲线为例比较​​gif​​包和​​animation​​模块实现动画的差异


from matplotlib import pyplot as plt
import numpy as np

t = np.linspace(0, 6, 100)
x = 16 * np.sin(t) ** 3
y = 13 * np.cos(t) - 5 * np.cos(2 * t) - 2 * np.cos(3 * t) - np.cos(4 * t)
fig = plt.figure(figsize=(5, 3), dpi=100)
plt.scatter(x, y)
plt.show()

心形曲线绘制


from matplotlib import pyplot as pltimport numpy as np
t = np.linspace(0, 6, 100)x = 16 * np.sin(t) ** 3y = 13 * np.cos(t) - 5 * np.cos(2 * t) - 2 * np.cos(3 * t) - np.cos(4 * t)fig = plt.figure(figsize=(5, 3), dpi=100)plt.scatter(x, y)plt.show()

Python通过matplotlib包和gif包生成gif动画

​gif​​包的实现方式


import numpy as np
import gif
from matplotlib import pyplot as plt

t = np.linspace(0, 6, 100)
x = 16 * np.sin(t) ** 3
y = 13 * np.cos(t) - 5 * np.cos(2 * t) - 2 * np.cos(3 * t) - np.cos(4 * t)

@gif.frame
def plot_love(x, y):
plt.figure(figsize=(5, 3), dpi=100)
plt.scatter(x, y, 60, c="r", alpha=0.7, marker=r"$\heartsuit$")
plt.axis("off")

frames = []
for i in range(1, len(x)):
of = plot_love(x[:i], y[:i])
frames.append(of)

gif.save(frames, "love.gif", duration=80)


import numpy as npimport giffrom matplotlib import pyplot as plt
t = np.linspace(0, 6, 100)x = 16 * np.sin(t) ** 3y = 13 * np.cos(t) - 5 * np.cos(2 * t) - 2 * np.cos(3 * t) - np.cos(4 * t)
@gif.framedef plot_love(x, y): plt.figure(figsize=(5, 3), dpi=100) plt.scatter(x, y, 60, c="r", alpha=0.7, marker=r"$\heartsuit$") plt.axis("off")frames = []for i in range(1, len(x)): of = plot_love(x[:i], y[:i]) frames.append(of)
gif.save(frames, "love.gif", duratinotallow=80)

Python通过matplotlib包和gif包生成gif动画

​matplotlib​​​ 常规​​FuncAnimation​​函数实现方式


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

t = np.linspace(0, 6, 100)
x = 16 * np.sin(t) ** 3
y = 13 * np.cos(t) - 5 * np.cos(2 * t) - 2 * np.cos(3 * t) - np.cos(4 * t)
data=[i for i in zip(x,y)]

def plot_love(data):
x, y = data
plt.scatter(x, y, 60, c="r", alpha=0.7, marker=r"$\heartsuit$")

fig=plt.figure(figsize=(5, 3), dpi=100)
plt.axis("off")
animator = animation.FuncAnimation(fig, plot_love, frames=data, interval=80)
animator.save("love.gif", writer='pillow')

​matplotlib​​​底层​​PillowWriter​​类实现方式

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

t = np.linspace(0, 6, 100)
x = 16 * np.sin(t) ** 3
y = 13 * np.cos(t) - 5 * np.cos(2 * t) - 2 * np.cos(3 * t) - np.cos(4 * t)


def plot_love(x, y):
plt.scatter(x, y, 60, c="r", alpha=0.7, marker=r"$\heartsuit$")


fig = plt.figure(figsize=(5, 3), dpi=100)
plt.axis("off")

writer = animation.PillowWriter(fps=15)
with writer.saving(fig, "love21.gif", dpi=100):
for i in range(1, len(x)):
plot_love(x[i], y[i])
writer.grab_frame()
from matplotlib import pyplot as pltimport matplotlib.animation as animationimport numpy as np
t = np.linspace(0, 6, 100)x = 16 * np.sin(t) ** 3y = 13 * np.cos(t) - 5 * np.cos(2 * t) - 2 * np.cos(3 * t) - np.cos(4 * t)

def plot_love(x, y): plt.scatter(x, y, 60, c="r", alpha=0.7, marker=r"$\heartsuit$")

fig = plt.figure(figsize=(5, 3), dpi=100)plt.axis("off")
writer = animation.PillowWriter(fps=15)with writer.saving(fig, "love21.gif", dpi=100): for i in range(1, len(x)): plot_love(x[i], y[i]) writer.grab_frame()

通过比较可知​gif​包的实现方式和​matplotlib​中利用​PillowWriter​实现方式类似,更偏底层一些,这样遇到比较复杂的绘图时更灵活。