freeze_graph.py

def freeze_graph(model_dir, output_node_names):
  """Extract the sub graph defined by the output nodes and convert 
  all its variables into constant 
  Args:
      model_dir: the root folder containing the checkpoint state file
      output_node_names: a string, containing all the output node's names, 
                          comma separated
                        """
  if not tf.gfile.Exists(model_dir):
    raise AssertionError(
      "Export directory doesn't exists. Please specify an export "
      "directory: %s" % model_dir)

  if not output_node_names:
    print("You need to supply the name of a node to --output_node_names.")
    return -1

  # We retrieve our checkpoint fullpath
  checkpoint = tf.train.get_checkpoint_state(model_dir)
  input_checkpoint = checkpoint.model_checkpoint_path
    
  # We precise the file fullname of our freezed graph
  absolute_model_dir = "/".join(input_checkpoint.split('/')[:-1])
  output_graph = absolute_model_dir + "/frozen_model.pb"

  # We clear devices to allow TensorFlow to control on which device it will load operations
  clear_devices = True

  # We start a session using a temporary fresh Graph
  with tf.Session(graph=tf.Graph()) as sess:
    # We import the meta graph in the current default Graph
    saver = tf.train.import_meta_graph(input_checkpoint + '.meta', clear_devices=clear_devices)

    # We restore the weights
    saver.restore(sess, input_checkpoint)

    # We use a built-in TF helper to export variables to constants
    output_graph_def = tf.graph_util.convert_variables_to_constants(
      sess, # The session is used to retrieve the weights
      tf.get_default_graph().as_graph_def(), # The graph_def is used to retrieve the nodes 
      output_node_names.split(",") # The output node names are used to select the usefull nodes
    ) 

    # Finally we serialize and dump the output graph to the filesystem
    with tf.gfile.GFile(output_graph, "wb") as f:
      f.write(output_graph_def.SerializeToString())
    print("%d ops in the final graph." % len(output_graph_def.node))

  return output_graph_def