title: Error ocurred when using tf.reduce_mean to compute the mean value of image
body: <p>When I tried to use tf.reduce_mean to compute the mean value of image for all axes, it showed that "An error ocurred while starting the kernel".</p>
  
  <p>Here is my code:</p>
  
  <pre><code>import tensorflow as tf
  import numpy as np
  imgdata = tf.read_file("./test_img/00000001.jpg")
  my_img = tf.image.decode_jpeg(imgdata)
  image = tf.reduce_mean(my_img)
  tf.Session().run(image)
  </code></pre>
  
  <p>I tried to run session to get "my_img" before computing mean, it didn't work as well.</p>
  
  <p>If I try to compute mean value of an array created by myself with the same shape, it goes well.</p>
  
  <pre><code>my_array = = np.random.randn(720, 1280, 3)
  tf.Session().run(tf.reduce_mean(my_array))
  </code></pre>