title: How to overlay level plots in R?
body: <p>In R, say you wish to present statistical data on an image background- like in medical imaging </p>
  
  <p><img src="https://i.stack.imgur.com/YoWtE.png" alt="example produced with Mango"></p>
  
  <p>Each layer is a different matrix. 
  Here is a non-sense example:</p>
  
  <ul>
  <li><code>volcano</code> in gray </li>
  <li><code>B&lt;- (volcano&gt;160) * rnorm(prod(dim(volcano))</code> in
  heat colors. </li>
  </ul>
  
  <p>How would you go about?</p>