Drawing circles on image with Matplotlib and NumPy

Question

I have NumPy arrays which hold circle centers.

import matplotlib.pylab as plt import numpy as np npX = np.asarray(X) npY = np.asarray(Y) plt.imshow(img) // TO-DO plt.show() 

How can I show circles at the given positions on my image?

Answer 1

You can do this with the matplotlib.patches.Circle patch.

For your example, we need to loop through the X and Y arrays, and then create a circle patch for each coordinate.

Here's an example placing circles on top of an image (from the matplotlib.cbook)

import matplotlib.pyplot as plt import numpy as np from matplotlib.patches import Circle  # Get an example image import matplotlib.cbook as cbook image_file = cbook.get_sample_data('grace_hopper.png') img = plt.imread(image_file)  # Make some example data x = np.random.rand(5)*img.shape[1] y = np.random.rand(5)*img.shape[0]  # Create a figure. Equal aspect so circles look circular fig,ax = plt.subplots(1) ax.set_aspect('equal')  # Show the image ax.imshow(img)  # Now, loop through coord arrays, and create a circle at each x,y pair for xx,yy in zip(x,y):     circ = Circle((xx,yy),50)     ax.add_patch(circ)  # Show the image plt.show() 

Answer 2

To get the image, instead of plt.show do (Without saving to disc one can get it as):

io_buf = io.BytesIO() fig.savefig(io_buf, format='raw')#dpi=36)#DPI) io_buf.seek(0) img_arr = np.reshape(np.frombuffer(io_buf.getvalue(), dtype=np.uint8),                          newshape=(int(fig.bbox.bounds[3]), int(fig.bbox.bounds[2]), -1)) io_buf.close() plt.close()  #To not display the image