title: Operations in Masked Numpy Arrays
body: <p>I have two masked numpy arrays. These are images.</p>
  
  <p>I am trying to subtract one from another. </p>
  
  <p>If I do the standard subtraction operator,</p>
  
  <pre><code>ma1 - ma2 
  </code></pre>
  
  <p>It will subtract them as if they were not masked (their masks are not considered). I would like them to subtract with their masks.</p>
  
  <p>Does anyone know how to subtract masked numpy arrays from eachother?</p>