private int getGrayFilterProperty(String prop) {
    GrayFilter filter = getGrayFilter();
    if ("brightness".equals(prop)) {
      return filter.getBrightness();
    }
    else if ("contrast".equals(prop)) {
      return filter.getContrast();
    }
    else if ("alpha".equals(prop)) {
      return filter.getAlpha();
    }
    throw new IllegalArgumentException("wrong property: " + prop);
  }
private int getGrayFilterProperty(String prop)