code: def postprocess_item(self, item: np_dict_type) -> np_dict_type:
      inp = item[INPUT_KEY].astype(np.float64)
      inp = (inp - self.mean) / self.std
      item[INPUT_KEY] = inp
      return item
  
imports: import numpy
  from typing import List
  from typing import Tuple
  from cftool.types import np_dict_type
  from ....schema import IRuntimeDataBlock
  from ....constants import INPUT_KEY
label_desc: Use image node_id 3 for calling the ImagenetNormalizeBlock obj's underlying member method code with example usage: obj.postprocess_item(item) and returns: item