docs: def _normalize_histogram2d(self, counts, type):
          """Normalize the values of the counts for a 2D histogram.
  
          This normalizes the values of a numpy array to the range 0-255.
  
          :param counts: a NumPy array which is to be rescaled.
          :param type: either 'bw' or 'reverse_bw'.
  
          """
          counts = (255 * (counts - np.nanmin(counts)) /
                    (np.nanmax(counts) - np.nanmin(counts)))
  
          if type == 'reverse_bw':
              counts = 255 - counts
  
          return counts.astype(np.uint8)