code: def posterize(img, bits_to_keep, **__):
      if bits_to_keep >= 8:
          return img
      return ImageOps.posterize(img, bits_to_keep)
  
imports: import math
  import numpy
  import random
  import re
  import PIL
  from PIL import Image, ImageEnhance, ImageOps
label_desc: Use image node_id 15 for calling a global function with example usage: posterize(img, bits_to_keep) and returns: ImageOps, img