为了将图形内容作为RGB像素值，matplotlib.backend_bases.Renderer需要首先绘制画布的内容。
您可以手动调用canvas.draw()来完成此操作：

from matplotlib.figure import Figure

fig = Figure()
canvas = fig.canvas
ax = fig.gca()

ax.text(0.0,0.0,"Test", fontsize=45)
ax.axis('off')

canvas.draw()  # Draw the canvas, cache the renderer

image_flat = np.frombuffer(canvas.tostring_rgb(), dtype='uint8')  # (H * W * 3,)
# NOTE: reversed converts (W, H) from get_width_height to (H, W)
image = image_flat.reshape(*reversed(canvas.get_width_height()), 3)  # (H, W, 3)

See here以获取有关Matplotlib API的更多信息。

对于正在搜索此问题答案的人来说，这是从以前的答案中收集的代码。请记住，np.fromstring方法已被弃用，而使用np.frombuffer。

#Image from plot
ax.axis('off')
fig.tight_layout(pad=0)

# To remove the huge white borders
ax.margins(0)

fig.canvas.draw()
image_from_plot = np.frombuffer(fig.canvas.tostring_rgb(), dtype=np.uint8)
image_from_plot = image_from_plot.reshape(fig.canvas.get_width_height()[::-1] + (3,))

从docs：
https://matplotlib.org/gallery/user_interfaces/canvasagg.html#sphx-glr-gallery-user-interfaces-canvasagg-py

fig = Figure(figsize=(5, 4), dpi=100)
# A canvas must be manually attached to the figure (pyplot would automatically
# do it).  This is done by instantiating the canvas with the figure as
# argument.
canvas = FigureCanvasAgg(fig)

# your plotting here

canvas.draw()
s, (width, height) = canvas.print_to_buffer()

# Option 2a: Convert to a NumPy array.
X = np.fromstring(s, np.uint8).reshape((height, width, 4))

我认为有一些更新，这是更容易。

canvas.draw()
buf = canvas.buffer_rgba()
X = np.asarray(buf)

文档的更新版本：

from matplotlib.backends.backend_agg import FigureCanvasAgg
from matplotlib.figure import Figure
import numpy as np

# make a Figure and attach it to a canvas.
fig = Figure(figsize=(5, 4), dpi=100)
canvas = FigureCanvasAgg(fig)

# Do some plotting here
ax = fig.add_subplot(111)
ax.plot([1, 2, 3])

# Retrieve a view on the renderer buffer
canvas.draw()
buf = canvas.buffer_rgba()
# convert to a NumPy array
X = np.asarray(buf)

要修复大边距Jorge引用，请添加ax.margins(0)。详情请看这里。