title: cv2.imread loads image as NoneType
body: <p>I have the following code attempting to show an image:</p>
  
  <pre><code>import cv2
  img = cv2.imread('img.tif',0)
  print(img.size)
  cv2.imshow('image',img)
  k = cv2.waitKey(0)
  if k == 27:         # wait for ESC key to exit
  cv2.destroyAllWindows()
  </code></pre>
  
  <p>which returns an error identifying 'img' as a NoneType object.</p>
  
  <p>In the same folder I have the same image converted to png via an online converter. Changing the second line to: </p>
  
  <pre><code>img = cv2.imread('img.png',0)
  </code></pre>
  
  <p>shows the image as expected.
  Also in the same folder I have a different .tif file. </p>
  
  <pre><code>img = cv2.imread('altimg.tif',0)
  </code></pre>
  
  <p>shows the alternate image as expected.</p>
  
  <p>This leads me to believe that path name is not my issue as is common with NoneType errors using imread. I have also tried using the full path name for each file. Again, the only issue came using 'img.tif'.</p>
  
  <p>'img.tif' opens with no issue in Windows Photo Viewer when opened from my file explorer. Here is that image:
  <a href="https://i.stack.imgur.com/C1mtP.png" rel="nofollow noreferrer">.tif image</a></p>
  
  <p>I am wondering if there are any other properties of the img.tif I may be overlooking that is preventing it from opening using OpenCV. The image is 640x800 pixels and the file size is 750 KB. I have not seen anything indicating that either of these parameters would cause an issue. 
  I am using Python3.6 64bit on Windows 10. Thanks for any suggestions.</p>