code: def build_backbone(cfg, input_shape=None):
      """
      Build a backbone from `cfg.MODEL.BACKBONE.NAME`.
  
      Returns:
          an instance of :class:`Backbone`
      """
      if input_shape is None:
          input_shape = ShapeSpec(channels=len(cfg.MODEL.PIXEL_MEAN))
  
      backbone_name = cfg.MODEL.BACKBONE.NAME
      backbone = BACKBONE_REGISTRY.get(backbone_name)(cfg, input_shape)
      assert isinstance(backbone, Backbone)
      return backbone
  
label_desc: Use image node_id 1 for calling a global function with example usage: build_backbone(cfg, input_shape) and returns: backbone