docs: def openning(input_rasterfilename, times):
          """Do openning.
  
          Openning: Erode firstly, then Dilate.
  
          Args:
              input_rasterfilename: input original raster image filename.
              times: Erode and Dilate times.
  
          Returns:
              openning_raster: raster image after open.
          """
          input_raster = RasterUtilClass.read_raster(input_rasterfilename)
          openning_raster = input_raster
          for i in range(times):
              openning_raster = RasterUtilClass.raster_erosion(openning_raster)
          for i in range(times):
              openning_raster = RasterUtilClass.raster_dilation(openning_raster)
          return openning_raster