title: Export image from R to word with alpha channel (transparency)
body: <p>I am wanting to export an R produced figure to Word. The figure contains transparency (alpha channel). Below is some example code - when exported to Windows metafile it throws an error:</p>
  
  <blockquote>
    <p>Warning message:
    In plot.xy(xy, type, ...) :
     semi-transparency is not supported on this device: reported only once per page</p>
  </blockquote>
  
  <p>Exporting to SVG produces the desired result, but this image format is not supported by MS Office. Is there a way around this? What image type could I use while retaining the alpha channel? PNG is possible, but this doesn't produce very crisp graphics - it loses the clear vectorized image. </p>
  
  <pre><code># Get some colours with transparency (alpha = 0.6)
  col.dot &lt;- rainbow(5, alpha = .6)
  
  # Save to svg file - OK
  svg("test_fig.svg")
  plot(1:5,col = col.dot, pch=15)
  dev.off()
  
  # Save to wmf - warning "semi-transparency is not supported on this device..."
  win.metafile("test_fig.wmf")
  plot(1:5,col = col.dot, pch=15)
  dev.off()
  </code></pre>
  
  <p>I should add, this is on a Windows system (Windows 8 64 bit, with Word 2013)</p>