matplotlib how to draw a rectangle on image

Question

How to draw a rectangle on an image  like this   import matplotlib pyplot as plt from PIL import Image import numpy as np im   np array Image open  dog png    dtype np uint8  plt imshow im   I don t know how to proceed

User · Answer

From my understanding matplotlib is a plotting library.

If you want to change the image data (e.g. draw a rectangle on an image), you could use PIL's ImageDraw, OpenCV, or something similar.

Here is PIL's ImageDraw method to draw a rectangle.

Here is one of OpenCV's methods for drawing a rectangle.

Your question asked about Matplotlib, but probably should have just asked about drawing a rectangle on an image.

Here is another question which addresses what I think you wanted to know: Draw a rectangle and a text in it using PIL

User · Answer

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

User · Answer

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

User · Answer

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

[python] matplotlib: how to draw a rectangle on image

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