title: Plotting a color histogram in python
body: <p>I have a jpeg image and want to plot a histogram of how frequently each color occurs in the image. I am able to generate a frequency table using pymorph.histogram(), but I don't know the actual color that each of the 256 colors indices correspond to. How can I generate this palette?<br>
  Further, is there an way to just generate a histogram plot of all these numbers, with the colors indicated (not a number in the range 0-255, but the actual color displayed)?</p>
  
  <p>My frequency list is generated using this code:</p>
  
  <pre><code>import pymorph
  import Image
  
  im=Image.open('image.jpg')
  im=np.asarray(im)
  hist_im=pymorph.histogram(im)
  </code></pre>