code: def preprocess(self, input_dicts, data_id, log_id):
      ((_, input_dict),) = input_dicts.items()
      inputs = []
      for key, data in input_dict.items():
          data = base64.b64decode(data.encode("utf8"))
          byte_stream = io.BytesIO(data)
          img = Image.open(byte_stream).convert("RGB")
          inputs.append(self.preprocess_pipeline(img))
      inputs = self.collate_inputs(inputs)
      return inputs, False, None, ""
  
imports: import copy
  from paddle_serving_server.web_service import WebService, Op
  from paddle_serving_server.proto import general_model_config_pb2
  import google.protobuf.text_format
  import os
  import numpy
  import base64
  from PIL import Image
  import io
  from preprocess_ops import Compose
  from postprocess_ops import HRNetPostProcess
  from argparse import ArgumentParser, RawDescriptionHelpFormatter
  import yaml
label_desc: Use image node_id 2 for calling the DetectorOp obj's underlying member method code with example usage: obj.preprocess(input_dicts, data_id, log_id) and returns: inputs,  False,  None,  str