title: Can Gnuplot handle png transparency?
body: <p>I'm using the <code>plot 'my_image.png' binary filetype=png with rgbimage</code> feature of gnuplot to superimpose images on a (scarce) scatterplot. </p>
  
  <p>My png's have a transparent background, so I had been hoping that they could 'respect' the grid and axes, but unfortunately they are plotted on top of it with a white, opaque background.</p>
  
  <p>Is there any ways to address this issue ?</p>
  
  <h3>Minimal working example</h3>
  
  <p>The file 2091450.png is provided by <a href="http://i35.tinypic.com/2091450.png" rel="nofollow">First Google result for Transparent PNG</a> : </p>
  
  <pre><code>set terminal pdfcairo font "CMU Serif" linewidth 4 rounded \
  fontscale 1.0 size 29.7cm, 21cm enhanced dashed
  set output 'transparency_test.pdf'
  
  set style line 81 lt rgb "#808080"
  set style line 80 lt 0  # dashed
  set style line 80 lt rgb "#808080"  # grey
  set grid back linestyle 80
  
  set border 3 back linestyle 81
  plot '2091450.png' binary filetype=png origin=(0,0) dx=1.0 dy=1.0 with rgbimage
  </code></pre>