code: def preprocess(self, left, right):
      x = tf.concat([left, right], axis=0)  # 2CHW
      rgb_mean = tf.reduce_mean(x, axis=[0, 2, 3], keep_dims=True)
      return (x - rgb_mean) / 255.0
  
imports: import tensorflow
  from tensorpack import ModelDesc, argscope, enable_argscope_for_module
label_desc: Use image node_id 4 for calling the FlowNetBase obj's underlying member method code with example usage: obj.preprocess(left, right) and returns: unknown