code: def optimize_nnp(graph_def):
      opt_graph = OptimizerBuilder(graph_def.default_graph())
      opt_parser = OptimizerParser(opt_graph)
      opt_graph.prepare()
      opt_parser.parse()
      return opt_graph.output()
  
label_desc: Use image node_id 1 for calling a global function with example usage: optimize_nnp(graph_def) and returns: opt_graph