code: def observation(self, frame):
      frame = cv2.cvtColor(frame, cv2.COLOR_RGB2GRAY)
      return frame[:, :, None]
  
imports: from collections import deque
  import cv2
  from .atari_wrappers import WarpFrame, ClipRewardEnv, FrameStack, ScaledFloatFrame
  from .wrappers import TimeLimit
  import numpy
  import gym
label_desc: Use image node_id 2 for calling the Rgb2gray obj's underlying member method code with example usage: obj.observation(frame) and returns: frame