halo_filter.py

#set the intensity of the halo
intensity = 250.0

#create a noramlizing constant so the halo fully fades out at the corners
denominator = intensity/((n/2)**2 + (m/2)**2)

#get the normalized squared distances of each pixel from the center
squared_distances = ((x-center_x)**2 + (y-center_y)**2)*denominator

#reshape this 2D matrix into a 3D matrix 
squared_distances = squared_distances.reshape(n,m,1)

#"stack" three copies of this 3D matrix to create a numpy array with the same dims as our image
stacked_squared_dists = np.concatenate([squared_distances]*3, axis=2)

#create an edited image by adding our original image to our halo
editedImg = img + stacked_squared_dists

#recast the edited image to integers
editedImg = editedImg.astype(int)

#show image
plt.imshow(editedImg)