public double getAverage()//ȼ   ϱ.
	{
		int i, j;
		double total = 0;
		for ( i = 0 ; i < width ; i ++ )
		{
			for ( j = 0 ; j < height ; j ++ )
			{
				total += pixel[i][j];
			}
		}
		return total/(width*height);
	}