title: Convert sRGB to Lab with convertColor?
body: <p>I'm trying to work with Lab colour, and need to do conversions from sRGB, ideally with R. I've just given <a href="http://stat.ethz.ch/R-manual/R-devel/library/grDevices/html/convertColor.html" rel="nofollow noreferrer" title="convertColor">convertColor</a> a go, and am a little confused. As a test, I'm converting the Macbeth ColorChecker swatches, but am not getting exactly the right values. </p>
  
  <p>Example:</p>
  
  <pre><code>swatch1sRGB &lt;- c(115,82,68)/255
  swatch1Lab &lt;- convertColor(swatch1sRGB, from="sRGB", to="Lab")
  swatch1Lab
              L      a.x        b
  [1,] 38.05293 11.86536 13.71442
  </code></pre>
  
  <p>Which is off the real values (37.986, 13.555, 14.059) by a reasonable margin of Macbeth ColorChecker values.</p>