code: private int updateProgress(int checkedTiles, int tilesNumber, int oldPercent, Collection<ImageBuffer> tiles)
      {
          final int percent = getProgressPercent(checkedTiles, tilesNumber);
          if (percent != oldPercent)
          {
              for (final ProgressListener listener : listeners)
              {
                  listener.notifyProgress(percent, tiles);
              }
          }
          return percent;
      }
docs: Update progress and notify if needed.
  
  @param checkedTiles The current number of checked tiles.
  @param tilesNumber The total number of tile to extract.
  @param oldPercent The old progress value.
  @param tiles The extracted tiles image.
  @return The last progress percent value.