Drawing circles on image with Matplotlib and NumPy

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

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