code: def _to_grayscale(self):
      return np.array(
          skimage.color.rgb2gray(self.frame_array) * 255, dtype="uint8"
      )
  
imports: import skimage.color
  import skimage.measure
  import skimage.transform
  import skimage.filters
  import skimage.morphology
  import numpy
  import io
  from PIL import Image
label_desc: Use image node_id 18 for calling the GameFrame obj's underlying member method code with example usage: obj._to_grayscale() and returns: np