code: def _normalize(self, img):
      img = img.astype(np.float32)
      img = (img / 255.0 - self.mean / 255.0) / (self.std / 255.0)
      return img
  
file_path: PaddleDetection/deploy/third_engine/demo_onnxruntime/infer_demo.py
imports: import cv2
  import numpy
  import argparse
  import onnxruntime
  from pathlib import Path
  from tqdm import tqdm
label_desc: Use image node_id 2 for calling the PicoDet obj's underlying member method code with example usage: obj._normalize(img) and returns: img