code: def preprocess(self, img_list):
      img_num = len(img_list)
      norm_img_batch = []
      max_wh_ratio = 0
      for ino in range(img_num):
          h, w = img_list[ino].shape[0:2]
          wh_ratio = w * 1.0 / h
          max_wh_ratio = max(max_wh_ratio, wh_ratio)
  
      for ino in range(img_num):
          norm_img = self.resize_norm_img(img_list[ino], max_wh_ratio)
          norm_img = norm_img[np.newaxis, :]
          norm_img_batch.append(norm_img)
      norm_img_batch = np.concatenate(norm_img_batch)
      norm_img_batch = norm_img_batch.copy()
  
      return norm_img_batch[0]
  
imports: import cv2
  import copy
  import numpy
  import math
  import re
  import sys
  import argparse
  import string
  from copy import deepcopy
label_desc: Use image node_id 3 for calling the OCRReader obj's underlying member method code with example usage: obj.preprocess(img_list) and returns: norm_img_batch