title: Extracting retina region from 2D images
body: <p>I am working on Diabetic Retinopathy detection. The database comprises of 2D images that looks like this one:</p>
  
  <p><a href="https://i.stack.imgur.com/kKBiU.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kKBiU.jpg" alt="Original Image"></a></p>
  
  <p>Now, I want to extract just the retina part from the images so that the final image looks like this one:</p>
  
  <p><a href="https://i.stack.imgur.com/LzvpV.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LzvpV.jpg" alt="New image"></a></p>
  
  <p>I have tried <code>Canny</code> and <code>HoughCircles</code> but it failed. Is there any way to extract this region using <code>OpenCv</code> or <code>scikit-image</code> or <code>PIL</code>?</p>