Draw Marker in Image

问题

I'm drawing a picture using Matplotlib:

plt.imshow(bild)
plt.show()

How do I add a Marker to this (eg. red dot / arrow) using the coordinates of the image?

回答1:

You can also use plt.scatter to add a red dot to mark the point. Building on the previous answer's example code:

import matplotlib.pyplot as plt
import numpy as np

img = np.random.randn(100, 100)

plt.figure()
plt.imshow(img)
plt.annotate('25, 50', xy=(25, 50), xycoords='data',
             xytext=(0.5, 0.5), textcoords='figure fraction',
             arrowprops=dict(arrowstyle="->"))
plt.scatter(25, 50, s=500, c='red', marker='o')
plt.show()

回答2:

You could use the module matplotlib.patches as shown below. Notice that in order to place a patch at the x^th row and y^th column of the image you need to reverse the order of the coordinates, i.e. y, x when instantiating the corresponding patch.

from skimage import io
import matplotlib.pyplot as plt
from matplotlib.patches import Arrow, Circle

maze = io.imread('https://i.stack.imgur.com/SQCy9.png')

ax, ay = 300, 25
dx, dy = 0, 75
cx, cy = 300, 750

patches = [Arrow(ay, ax, dy, dx, width=100., color='green'),
           Circle((cy, cx), radius=25, color='red')]

fig, ax = plt.subplots(1)
ax.imshow(maze)
for p in patches:
    ax.add_patch(p)
plt.show(fig)

回答3:

You can use the function plt.annotate for this:

import matplotlib.pyplot as plt
import numpy as np

img = np.random.randn(100, 100)

plt.imshow(img)
plt.annotate('25, 50', xy=(25, 40), xycoords='data',
             xytext=(0.5, 0.5), textcoords='figure fraction',
             arrowprops=dict(arrowstyle="->"))
plt.show()

来源：https://stackoverflow.com/questions/32551536/draw-marker-in-image