title: PIL open tif image only one channel
body: <p>There are two situations when I open tif image by PIL. First one is a normal one that can open an image as RGB and display by plt well. However, the second one as shown in the codes below:</p>
  
  <pre><code>from PIL import Image
  import numpy as np
  import matplotlib.pyplot as plt
  img = Image.open('test1.tif')
  a = np.array(img)
  a.shape
  # output: (2040,2040)
  </code></pre>
  
  <p>can only open as a shape of (2040,2040), the previous one with a shape of (2040,2040,3). When I convert the (2040,2040) one into RGB mode using <code>img = img.convert('RGB')</code> and showing it via plt only saw a blank square.</p>
  
  <p>Please, somebody, tell me what is going wrong? 
  Thanks in advance!</p>
  
  <p>Original Image:
  <a href="https://i.stack.imgur.com/fD3kM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fD3kM.png" alt="enter image description here"></a></p>
  
  <p>And numpy array:</p>
  
  <pre><code>array([[7256, 6926, 7270, ..., 7368, 7457, 7555],
     [7174, 6945, 6878, ..., 7401, 7353, 7895],
     [7288, 7099, 7140, ..., 7359, 7524, 7587],
     ...,
     [6769, 6695, 6698, ..., 6599, 6788, 6898],
     [6780, 6683, 6857, ..., 6723, 6761, 6861],
     [6788, 6626, 6761, ..., 6738, 6751, 7054]], dtype=uint16)
  </code></pre>
  
  <p>After convert to RGB mode:
  <a href="https://i.stack.imgur.com/rorv3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rorv3.png" alt="enter image description here"></a>
  numpy array:</p>
  
  <pre><code>array([[[255, 255, 255],
          [255, 255, 255],
          [255, 255, 255],
          ...,
          [255, 255, 255],
          [255, 255, 255],
          [255, 255, 255]]], dtype=uint8)
  </code></pre>