public Object getValueAt(int rowIndex, int columnIndex) {
		Overlay overlay = overlays.get(rowIndex);
		switch (columnIndex) {
			case 0: return overlay.isVisible();
			case 1: return overlay.getColor();
			case 2: return overlay.getName();
			case 3: return overlay.getAlpha();
			default: break;
		}
		return null;
	}