title: rgb2gray not working, creating rainbow image
body: <p>I'm trying to do data analysis on a series of photos, and when all photos are "changed" to grayscale from RGB, they are coming up as, well look:</p>
  
  <p><a href="http://i.stack.imgur.com/3vjpH.png" rel="nofollow">The standard Astronaut image as my system says it's grayscale</a></p>
  
  <p>Here's the code I'm using:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  from skimage.color import rgb2gray
  from skimage import data
  img = data.astronaut()
  img_gray = rgb2gray(img)
  
  plt.imshow(img_gray)
  plt.show()
  </code></pre>
  
  <p>I also tried converting as hsv to rgb then grayscale, but it still produces a similar, non-grayscale image. </p>