title: Colorize a grayscale image
body: <p>I have a grayscale image that needs to be painted with values from a gradient of 5 colors. Light pixels should get a lighter color from the gradient, dark pixels should get a darker one.</p>
  
  <p>If the gradient starts with yellow and ends with red, then white pixels would be yellow and black pixels red with everything in between along the gradient.</p>
  
  <p>Can it be done with ColorMatrix?</p>