Matplotlib 图以图像为 numpy 数组

Question

我正在尝试从 Matplotlib 图形中获取一个 numpy 数组图像，我目前正在通过保存到一个文件，然后重新读取该文件来做到这一点，但我觉得必须有更好的方法。这是我现在正在做的事情：

from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure

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

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

canvas.print_figure("output.png")
image = plt.imread("output.png")

我试过了：

image = np.fromstring( canvas.tostring_rgb(), dtype='uint8' )

从我找到的一个示例中，但它给了我一个错误，说“FigureCanvasAgg”对象没有属性“renderer”。

Answer 1

为了得到图形内容为RGB像素值，matplotlib.backend_bases.Renderer需要先绘制canvas的内容。你可以手动调用canvas.draw()：

from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure

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

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

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

image = np.frombuffer(canvas.tostring_rgb(), dtype='uint8')

See here 了解有关 Matplotlib API 的更多信息。

Answer 2

来自文档：

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))

Answer 3

对于正在搜索此问题的答案的人，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，而改用 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,))

Answer 4

要修复 Jorge 引用的大边距，请添加 ax.margins(0)。详情请见here。

Answer 5

我认为有一些更新，这更容易。

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

文档中的更新版本：

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)