title: Error using cv2.equalizeHist
body: <p>I am trying to equalize the histogram of a gray level image using the following code:</p>
  
  <pre><code>import cv2
  im = cv2.imread("myimage.png")
  eq = cv2.equalizeHist(im)
  </code></pre>
  
  <p>The following exception is raised:</p>
  
  <pre><code>error: (-215) CV_ARE_SIZES_EQ(src, dst) &amp;&amp; CV_ARE_TYPES_EQ(src, dst) &amp;&amp; CV_MAT_TYPE(src-&gt;type) == CV_8UC1 in function cvEqualizeHist
  </code></pre>
  
  <p>The version of opencv is <code>2.4.2</code></p>
  
  <p>Any guesses?</p>