private double getCov()
	{
	
		int i, j;
		double cov = 0;
		for ( i = 0 ; i < orig.getWidth() ; i ++ )
		{
			for ( j = 0 ; j < orig.getHeight() ; j ++ )
			{
				cov += (orig.getlum(i, j) - avg_or) * (target.getlum(i, j) - avg_ta);
			}
		}
		
		return cov;
	}