python – matplotlib: how to draw a rectangle on image

python – matplotlib: how to draw a rectangle on image

You can add a Rectangle patch to the matplotlib Axes.

For example (using the image from the tutorial here):

import matplotlib.pyplot as plt
import matplotlib.patches as patches
from PIL import Image

im = Image.open(stinkbug.png)

# Create figure and axes
fig, ax = plt.subplots()

# Display the image
ax.imshow(im)

# Create a Rectangle patch
rect = patches.Rectangle((50, 100), 40, 30, linewidth=1, edgecolor=r, facecolor=none)

# Add the patch to the Axes
ax.add_patch(rect)

plt.show()

enter

There is no need for subplots, and pyplot can display PIL images, so this can be simplified further:

import matplotlib.pyplot as plt
from matplotlib.patches import Rectangle
from PIL import Image

im = Image.open(stinkbug.png)

# Display the image
plt.imshow(im)

# Get the current reference
ax = plt.gca()

# Create a Rectangle patch
rect = Rectangle((50,100),40,30,linewidth=1,edgecolor=r,facecolor=none)

# Add the patch to the Axes
ax.add_patch(rect)

Or, the short version:

import matplotlib.pyplot as plt
from matplotlib.patches import Rectangle
from PIL import Image

# Display the image
plt.imshow(Image.open(stinkbug.png))

# Add the patch to the Axes
plt.gca().add_patch(Rectangle((50,100),40,30,linewidth=1,edgecolor=r,facecolor=none))

python – matplotlib: how to draw a rectangle on image

You need use patches.

import matplotlib.pyplot as plt
import matplotlib.patches as patches

fig2 = plt.figure()
ax2 = fig2.add_subplot(111, aspect=equal)

ax2.add_patch(
     patches.Rectangle(
        (0.1, 0.1),
        0.5,
        0.5,
        fill=False      # remove background
     ) ) 
fig2.savefig(rect2.png, dpi=90, bbox_inches=tight)

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