title: matplotlib image shows in black and white, but I wanted gray
body: <p>I have a small code sample to plot images in matplotlib, and the image is shown as this :</p>
  
  <p><a href="https://i.stack.imgur.com/r4CPR.png" rel="nofollow"><img src="https://i.stack.imgur.com/r4CPR.png" alt="enter image description here"></a></p>
  
  <p>Notice the image in the black box has black background, while my desired output is this :</p>
  
  <p><a href="https://i.stack.imgur.com/0jNcL.png" rel="nofollow"><img src="https://i.stack.imgur.com/0jNcL.png" alt="enter image description here"></a></p>
  
  <p>My code to plot the image is this :</p>
  
  <pre><code>plt.subplot(111)
  plt.imshow(np.abs(img), cmap = 'gray')
  plt.title('Level 0'), plt.xticks([]), plt.yticks([])
  plt.show()
  </code></pre>
  
  <p>My understanding is that <code>cmap=grey</code> should display it in grayscale. Below is a snippet of the matrix <code>img</code> being plotted :</p>
  
  <pre><code>[[ 192.77504036 +1.21392817e-11j  151.92357434 +1.21278246e-11j
     140.67585733 +6.71014111e-12j  167.76903747 +2.92050743e-12j
     147.59664180 +2.33718944e-12j   98.27986577 +3.56896094e-12j
      96.16252035 +5.31530804e-12j  112.39194666 +5.86689097e-12j....
  </code></pre>
  
  <p>What am I missing here ?</p>