code: def init_op(self):
      self.det_preprocess = Sequential(
          [
              DetResizeForTest(),
              Div(255),
              Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225]),
              Transpose((2, 0, 1)),
          ]
      )
      self.filter_func = FilterBoxes(10, 10)
      self.post_func = DBPostProcess(
          {
              "thresh": 0.3,
              "box_thresh": 0.5,
              "max_candidates": 1000,
              "unclip_ratio": 1.5,
              "min_size": 3,
          }
      )
  
file_path: PaddleOCR/deploy/pdserving/web_service_det.py
imports: from paddle_serving_server.web_service import WebService, Op
  import logging
  import numpy
  import cv2
  import base64
  from ocr_reader import OCRReader, DetResizeForTest, ArgsParser
  from paddle_serving_app.reader import Sequential, ResizeByFactor
  from paddle_serving_app.reader import Div, Normalize, Transpose
  from paddle_serving_app.reader import DBPostProcess, FilterBoxes, GetRotateCropImage, SortedBoxes
label_desc: Use image node_id 1 for calling the DetOp obj's underlying member method code with example usage: obj.init_op() without return types