Agg缓冲区
使用后端AGG以RGB字符串的形式访问地物画布，然后将其转换为数组并将其传递给Pillow进行渲染。
import numpy as np
from matplotlib.backends.backend_agg import FigureCanvasAgg
import matplotlib.pyplot as plt
plt.plot([1, 2, 3])
canvas = plt.get_current_fig_manager().canvas
agg = canvas.switch_backends(FigureCanvasAgg)
agg.draw()
s, (width, height) = agg.print_to_buffer()
# Convert to a NumPy array.
X = np.fromstring(s, np.uint8).reshape((height, width, 4))
# Pass off to PIL.
from PIL import Image
im = Image.frombytes("RGBA", (width, height), s)
# Uncomment this line to display the image using ImageMagick's `display` tool.
# im.show()