title: Image overlay with matrix
body: <p>I have an image (png) that I want to put underneath a heatmap(so to speak) made from a and a 2D matrix of values 0-1. So the intensity of the spot would be decided by how large the value in the matrix is. </p>
  
  <p>I can use imshow(matrix) but that completely draws over the image underneath. Is it possible to perhaps, not draw any pixels with matrix values &lt;.05 or some other way to make this work?</p>