code: def observation(self, frame):
      frame = cv2.cvtColor(frame, cv2.COLOR_RGB2GRAY)
      frame = cv2.resize(
          frame, (self.width, self.height), interpolation=cv2.INTER_AREA
      )
      return frame
  
imports: import time
  import numpy
  from collections import deque
  import gym
  from gym import spaces
  from parl.env.compat_wrappers import CompatWrapper, is_gym_version_ge, V_NPRANDOM_CHANGED
  import cv2
label_desc: Use image node_id 4 for calling the WarpFrame obj's underlying member method code with example usage: obj.observation(frame) and returns: frame