title: Slice or split a input image tensor into variable based on the channel
body: <p>I was trying to slice or split a tensor of input image of shape[batch_size,256,256,3] into three separate variable of shape [batch_size,256,256,1] where each variable contains exactly one channel of the input image , i.e</p>
  
  <p>R_channel=image[-1,256,256,0]</p>
  
  <p>G_channel=image[-1,256,256,1]</p>
  
  <p>B_channel=image[-1,256,256,2]</p>
  
  <p>i have tried the following code for the above:</p>
  
  <pre><code>imgs, label = iterator.get_next()
  
  channel_r=imgs[-1,:,:,0]
  channel_g=imgs[-1,:,:,1]
  channel_b=imgs[-1,:,:,2]
  NN_network(imgs,channel_r,channel_g,channel_b)
  ...
  def NN_network(imgs,c_r,c_g,c_b):
      conv1=tf.layers.conv2d(imgs,n_filter,kernel_Size,...)
      conv2=tf.layers.conv2d(c_r,n_filter,kernel_Size,...)
      conv3=tf.layers.conv2d(c_g,n_filter,kernel_Size,...)
      conv4=tf.layers.conv2d(c_b,n_filter,kernel_Size,...)
      concat_layer=tf.concat(axis=3,values=[imgs,c_r,c_g,c_b])
  </code></pre>
  
  <p>in tensorflow but i get the following error:</p>
  
  <blockquote>
    <p>InvalidArgumentError (see above for traceback): ConcatOp : Dimensions
    of inputs should match: shape[0] = [16,12,256,256] vs. shape[1] =
    [1,12,256,256]     [[node LC_Nikon1/concat (defined at )  =
    ConcatV2[N=4, T=DT_FLOAT, Tidx=DT_INT32,
    _device="/job:localhost/replica:0/task:0/device:GPU:0"](/conv2d/BiasAdd,
    /conv2d_1/BiasAdd, /conv2d_2/BiasAdd, /conv2d_3/BiasAdd,
    gradients/resize_image_with_crop_or_pad_1/crop_to_bounding_box/Slice_grad/concat/axis)]]
       [[{{node
    resize_image_with_crop_or_pad/pad_to_bounding_box/GreaterEqual_3/_83}}
    = _Recvclient_terminated=false, recv_device="/job:localhost/replica:0/task:0/device:CPU:0",
    send_device="/job:localhost/replica:0/task:0/device:GPU:0",
    send_device_incarnation=1,
    tensor_name="edge_384_resize_image_with_crop_or_pad/pad_to_bounding_box/GreaterEqual_3",
    tensor_type=DT_BOOL,
    _device="/job:localhost/replica:0/task:0/device:CPU:0"]]</p>
  </blockquote>
  
  <p>How can i do the follwoing concat, what is this error for?</p>