title: How to display the code of an image after tf.decode_image
body: <p>I'm trying to see how the tf decode images so I try</p>
  
  <pre><code>import tensorflow as tf
  image1 = tf.image.decode_png('/usr/src/pycharm-2017.1/bin/pycharm.png')
  print(image1.shape)
  with tf.Session() as sess:
      img = sess.run(image1)
      print(img.shape, img)
  </code></pre>
  
  <p>but it raise the error</p>
  
  <pre><code>InvalidArgumentError (see above for traceback): Invalid PNG header, data size 39
   [[Node: DecodePng = DecodePng[channels=0, dtype=DT_UINT8, _device="/job:localhost/replica:0/task:0/cpu:0"](DecodePng/contents)]]
  </code></pre>
  
  <p>Also I've tried  tf.image.decode_image, but it didn't work either.
  What's wrong ? How can I fix it?
  Thank u</p>