code: def blackwhite(clip, RGB=None, preserve_luminosity=True):
      """Desaturates the picture, makes it black and white.
      Parameter RGB allows to set weights for the different color
      channels.
      If RBG is 'CRT_phosphor' a special set of values is used.
      preserve_luminosity maintains the sum of RGB to 1.
      """
      if RGB is None:
          RGB = [1, 1, 1]
  
      if RGB == "CRT_phosphor":
          RGB = [0.2125, 0.7154, 0.0721]
  
      R, G, B = (
          1.0 * np.array(RGB) / (sum(RGB) if preserve_luminosity else 1)
      )
  
      def filter(im):
          im = R * im[:, :, 0] + G * im[:, :, 1] + B * im[:, :, 2]
          return np.dstack(3 * [im]).astype("uint8")
  
      return clip.image_transform(filter)
  
label_desc: Use image node_id 1 for calling a global function with example usage: blackwhite(clip, RGB, preserve_luminosity) and returns: clip, np