title: Showing an image with pylab.imshow()
body: <p>I'm relatively new to all this and I started the tutorial on image analysis <a href="http://www.pythonvision.org/basic-tutorial" rel="nofollow noreferrer">here</a>. When trying to perform the <code>pylab.imshow(dna)</code> step it returns the following error:</p>
  <pre><code>In [10]: pylab.imshow(dna)
  ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  &lt;ipython-input-10-fc86cadb4e46&gt; in &lt;module&gt;()
  ----&gt; 1 pylab.imshow(dna)
  
   /usr/lib/pymodules/python2.7/matplotlib/pyplot.pyc in imshow(X, cmap, norm, aspect,    interpolation, alpha, vmin, vmax, origin, extent, shape, filternorm, filterrad, imlim, resample, url, hold, **kwargs)
     2375         ax.hold(hold)
     2376     try:
  -&gt; 2377         ret = ax.imshow(X, cmap, norm, aspect, interpolation, alpha, vmin, vmax, origin, extent, shape, filternorm, filterrad, imlim, resample, url, **kwargs)
     2378         draw_if_interactive()
     2379     finally:
  
  /usr/lib/pymodules/python2.7/matplotlib/axes.pyc in imshow(self, X, cmap, norm, aspect, interpolation, alpha, vmin, vmax, origin, extent, shape, filternorm, filterrad, imlim, resample, url, **kwargs)
     6794                        filterrad=filterrad, resample=resample, **kwargs)
     6795 
  -&gt; 6796         im.set_data(X)
     6797         im.set_alpha(alpha)
     6798         self._set_artist_props(im)
  
  /usr/lib/pymodules/python2.7/matplotlib/image.pyc in set_data(self, A)
      409         if (self._A.ndim not in (2, 3) or
      410             (self._A.ndim == 3 and self._A.shape[-1] not in (3, 4))):
  --&gt; 411             raise TypeError(&quot;Invalid dimensions for image data&quot;)
      412 
      413         self._imcache =None
  
  TypeError: Invalid dimensions for image data
  </code></pre>
  <p>Fairly certain I have followed all the instructions in the tutorial to the letter but I can't work out was is going wrong.</p>