code: public Collection<ImageBuffer> extract(int tw, int th, Collection<Media> levelRips)
      {
          return extract(null, tw, th, levelRips);
      }
docs: Start using specified output file. Listeners are cleared once ended.
  
  @param tw The tile width.
  @param th The tile height.
  @param levelRips The levels rip used.
  @return The extracted tile sheets.
  @throws LionEngineException If an error occurred when computing sheet.