code: def _is_gray_image(tens: Tensor):
      # tens = to_tensor(tens)
      # return tens.is_gray()
      return (len(tens.shape) == 2) or (
          len(tens.shape) == 3 and tens.shape[-1] == 1
      )
  
file_path: caer/caer/color/_gray.py
imports: import cv2
  from ..coreten import Tensor, to_tensor
  from ._constants import GRAY2BGR, GRAY2RGB
  from ._bgr import bgr2lab, bgr2hsv, bgr2hls, bgr2yuv, bgr2luv
label_desc: Use image node_id 1 for calling a global function with example usage: _is_gray_image(tens) and returns: unknown