docstr: Resize image to target size, convert normalized xywh to pixel xyxy
  format ([x_center, y_center, width, height] -> [x0, y0, x1, y1]).
  Args:
      target_size (int|list): image target size.
code: def __init__(self, target_size):
      """
      Resize image to target size, convert normalized xywh to pixel xyxy
      format ([x_center, y_center, width, height] -> [x0, y0, x1, y1]).
      Args:
          target_size (int|list): image target size.
      """
      super(LetterBoxResize, self).__init__()
      if not isinstance(target_size, (Integral, Sequence)):
          raise TypeError(
              "Type of target_size is invalid. Must be Integer or List or Tuple, now is {}".format(
                  type(target_size)
              )
          )
      if isinstance(target_size, Integral):
          target_size = [target_size, target_size]
      self.target_size = target_size
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from numbers import Integral
  import cv2
  import copy
  import numpy
  import random
  import math
  from .operators import BaseOperator, register_op
  from .batch_operators import Gt2TTFTarget
  from ppdet.modeling.bbox_utils import bbox_iou_np_expand
  from ppdet.utils.logger import setup_logger
  from .op_helper import gaussian_radius
label_desc: Use image node_id 1 to create a new LetterBoxResize object from inherited base classes: BaseOperator with example: obj = LetterBoxResize(target_size)