code: def get_columns_rows(filenames):
      
      tiles = []
      for filename in filenames:
          row, column = os.path.splitext(filename)[0][-5:].split('_')
          tiles.append((int(row), int(column)))
      rows = [pos[0] for pos in tiles]; columns = [pos[1] for pos in tiles]
      num_rows = max(rows); num_columns = max(columns)
      return (num_columns, num_rows)
docs: Derive number of columns and rows from filenames.