title: Tensorflow dense_image_warp Failed to convert object of type <type 'list'> to Tensor
body: <p>Using up-to-date Keras and Tensorflow on Ubuntu 16.04 and 14.04. For the following code:</p>
  
  <pre><code>img2D = Input(shape=(100, 100, 3))
  refPosX = Input(shape=(100, 100, 1))
  refPosY = Input(shape=(100, 100, 1))
  # refImg = Input(shape=(100, 100, 3))
  
  # Passing values to depth net
  depth_map = depth_net(dFeatures)
  curX = tf.multiply(depth_map, refPosX)
  # curY = K.dot(depth_map, refPosY)
  curY = tf.multiply(depth_map, refPosY)
  # dMove = concatenate([curX, curY])
  dMove = tf.concat([curX, curY], axis=3)
  
  warped = tfc.image.dense_image_warp(img2D, dMove)
  </code></pre>
  
  <p>I'm receiving the error output:</p>
  
  <pre><code>Using TensorFlow backend.
  Traceback (most recent call last):
  File "/home/carson/ws/dla/test_network_5/depth_and_color_nets.py", line 89, in &lt;module&gt;
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/contrib/image/python/ops/dense_image_warp.py", line 195, in dense_image_warp
      [batch_size, height * width, 2])
   File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/ops/gen_array_ops.py", line 6482, in reshape
  "Reshape", tensor=tensor, shape=shape, name=name)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/framework/op_def_library.py", line 513, in _apply_op_helper
  raise err
  TypeError: Failed to convert object of type &lt;type 'list'&gt; to Tensor. Contents: [None, 10000, 2]. Consider casting elements to a supported type.
  </code></pre>
  
  <p>I'm a bit confused as I don't know where I'm going wrong here. Why would the elements not be of a supported type? At what point am I passing a list object to the function?</p>