code: def normalize(self, im):
      img_mean = [0.485, 0.456, 0.406]
      img_std = [0.229, 0.224, 0.225]
      im = im.astype(np.float32, copy=False)
      im = im / 255
      im -= img_mean
      im /= img_std
      channel_swap = (2, 0, 1)
      im = im.transpose(channel_swap)
      return im
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import sys
  import cv2
  import numpy
  import pyclipper
  from PIL import ImageDraw
  from shapely.geometry import Polygon
label_desc: Use image node_id 3 for calling the DBPreProcess obj's underlying member method code with example usage: obj.normalize(im) and returns: im