code: def posterize(tens: Tensor, bits: int) -> Tensor:
      r"""Reduce the number of bits for each color channel in the image.
  
      Args:
          tens (Tensor): Image to posterize.
          bits (int): Number of high bits. Must be in range [0, 8]
  
      Returns:
          Image with reduced color channels (Tensor)
  
      Examples::
  
          >> tens = caer.data.sunrise()
          >> posterized = caer.posterize(tens, bits=4)
          >> posterized.shape
          (427,640,3)
  
      """
      tens = to_tensor(tens, override_checks=True)
      bits = np.uint8(bits)
  
      if tens.dtype != np.uint8:
          raise TypeError("Image must have uint8 channel type")
  
      if np.any((bits < 0) | (bits > 8)):
          raise ValueError("bits must be in range [0, 8]")
  
      if not bits.shape or len(bits) == 1:  # type: ignore[arg-type, attr-defined]
          if bits == 0:
              return np.zeros_like(tens)
          if bits == 8:
              return tens.copy()
  
          lut = np.arange(0, 256, dtype=np.uint8)
          mask = ~np.uint8(2 ** (8 - bits) - 1)
          lut &= mask
  
          return to_tensor(cv.LUT(tens, lut), override_checks=True)
  
      if not _is_rgb_image(tens):
          raise TypeError("If `bits` is iterable, image must be RGB")
  
      result_tens = np.empty_like(tens)
      for i, channel_bits in enumerate(bits):  # type: ignore[arg-type, var-annotated]
          if channel_bits == 0:
              result_tens[..., i] = np.zeros_like(tens[..., i])
          elif channel_bits == 8:
              result_tens[..., i] = tens[..., i].copy()
          else:
              lut = np.arange(0, 256, dtype=np.uint8)
              mask = ~np.uint8(2 ** (8 - channel_bits) - 1)
              lut &= mask
  
              result_tens[..., i] = cv.LUT(tens[..., i], lut)
  
      return to_tensor(result_tens, override_checks=True)
  
imports: import numpy
  import cv2
  import random
  import collections
  from ..coreten import Tensor, to_tensor
  from .._internal import _check_target_size
  from ..globals import INTER_AREA, INTER_CUBIC, INTER_NEAREST, INTER_LINEAR
  from ..annotations import Union, Tuple, Optional
label_desc: Use image node_id 19 for calling a global function with example usage: posterize(tens, bits) and returns: to_tensor, to_tensor, np, tens