title: Area segmentation within a segmented area
body: <p>Here's an image:</p>
  
  <p><img src="https://i.stack.imgur.com/bNseT.png" alt="enter image description here"></p>
  
  <p>I would like to know how i can set the <strong>black circle to white and the rest to black.</strong></p>
  
  <p>(So segment the black circle within the white area).</p>
  
  <p>I know i can invert the image and the circle will be white ... but so will the entire black part that is seen in this image.</p>
  
  <p>If i would have to do this in matlab i would do a connected component operation and check the circularity of the BLOBs. Though I have to do this in opencv (javacv to be precise.)</p>
  
  <p>Is there an easy way of doing this in opencv (javacv).</p>
  
  <p>Thx in advance</p>