title: Filling out the remaining region with the pixel value "0"
body: <p>In the following image, I have filled two regions with two different shades:</p>
  
  <p><img src="https://i.stack.imgur.com/5Yo8l.png" alt="enter image description here"></p>
  
  <p>How can I fill the <strong>remaining</strong> part of the image (parts not filled) with the pixel values <code>0</code> (black) in <code>MATLAB</code>?</p>
  
  <p>Thanks.</p>