title: Problems with repeat use of crop method in Pillow (Python's PIL fork)
body: <p>I have some code that splits a single image into multiple sub-images using Pillow's <em>crop</em> method. My code is similar to the following:</p>
  
  <pre><code>from PIL import Image
  from PIL import ImageTk
  import Tkinter    
  
  
  # Open image from file path
  baseimg = Image.open("PathToLargeImage.tif")
  
  # Get image attributes
  height = baseimg.height
  width = baseimg.width
  
  # Create a list of sub-images
  subimages = []
  for y in range(0, height, 50):
      subimage = baseimg.crop((0, y, width, 10))
      subimage.load()  # Call load on sub-image to detach it from baseimg
      subimages.append(subimage)
      showimage(subimage)
  </code></pre>
  
  <p>When I make a call to display <strong>subimage</strong> the first sub-image will display properly, then all the following sub-images will have a zero height (discovered from debugging with PyCharm) and display improperly.</p>
  
  <p>The <em>showimage</em> function uses Tkinter and is as follows:</p>
  
  <pre><code>def showimage(img):
      # Build main window
      root = Tkinter.Tk()
      # Convert image
      tkimage = ImageTk.PhotoImage(img)
      # Add image on window
      Tkinter.Label(root, image=tkimage).pack()
      # Start gui loop
      root.mainloop()
  </code></pre>