title: imagemagick remove clusters of pixels
body: <p>Original image:</p>
  
  <p><img src="https://i.stack.imgur.com/nKUzd.jpg" alt="enter image description here"></p>
  
  <p>I want to isolate and remove (i.e. turn to white) small clumps of pixels with large amounts of white space around them. Examples of pixel areas I would like to turn to white:</p>
  
  <p><img src="https://i.stack.imgur.com/gmyjf.jpg" alt="enter image description here"></p>
  
  <p>The goal is to get larger unbroken areas of white space. Example of the final result:</p>
  
  <p><img src="https://i.stack.imgur.com/7EHYD.jpg" alt="enter image description here"></p>