code: def opacity_transfer_function(key, n_colors):
      
      transfer_func = {
          'linear': np.linspace(0, 255, n_colors, dtype=np.uint8),
          'linear_r': np.linspace(0, 255, n_colors, dtype=np.uint8)[::-1],
          'geom': np.geomspace(1e-6, 255, n_colors, dtype=np.uint8),
          'geom_r': np.geomspace(255, 1e-6, n_colors, dtype=np.uint8),
      }
      try:
          return transfer_func[key]
      except KeyError:
          raise KeyError('opactiy transfer function ({}) unknown.'.format(key))
docs: Get the opacity transfer function results: range from 0 to 255