code: def posterize_func(img, bits):
      """
      same output as PIL.ImageOps.posterize
      """
      out = np.bitwise_and(img, np.uint8(255 << (8 - bits)))
      return out
  
imports: import cv2
  import numpy
  import torch
label_desc: Use image node_id 13 for calling a global function with example usage: posterize_func(img, bits) and returns: out