title: Filling an outlined circle
body: <p>I have a collection of images with a circle drawn as a white outline. However, I want to fill the complete circle with white color. What is a fast way to do it? The following is the sample of the image:</p>
  
  <p><img src="https://i.stack.imgur.com/BLYmz.png" alt="Sample image"></p>
  
  <p>I have tried using nested loops to achieve this, but it takes a lot of time, and I have around 1.5 million images. The following is my code:</p>
  
  <pre><code>roundRobinIndex = 0
  new_image = np.zeros((img_w, img_h))
  for row in range(540):
      for column in range(800):
          if image[row,column] == 255:
              roundRobinIndex = (roundRobinIndex + 1) % 2
          if roundRobinIndex == 1:
              new_image[row, column] = 255
  </code></pre>