title: Matlab: Overlaying only the contour plot lines on an imagesc
body: <p>With two matrices of equal size, one representing certain values as a contour plot, and the other a gray and white plot representing the statistical significance of such values (binary values of 0 or 1) as an imagesc plot, I would like to combine them so that I only have the (black) contour lines on top of my white and gray imagesc plot.</p>
  
  <p>So I have two 32x87 matrices:
  anomaly
  testResults</p>
  
  <p>Here is the relevant portion of my code:</p>
  
  <pre><code>figure
  imagesc(testResults.')
  colormap(gray)
  colorbar
  caxis([-2 1])
  hold on
  clabel(contour(anomaly.'))
  colormap(gray)
  hold off
  </code></pre>
  
  <p>So one problem is that I cannot find a way to set limits on my contour line colors to keep them all black (since I have clabel, I don't need any variation). Another odd problem I am having is that if I don't use the transpose of anomaly (anomaly.'), it will not show up on this plot. Any help is greatly appreciated.</p>
  
  <p>I have tried playing around with transparency, but it had been really difficult to see much, though I won't rule it out.</p>