c#中图片合并后保存的问题

pictureBox1.Image=Image.FromFile(@"E:\1.bmp");
Graphics g=Graphics.FromImage(pictureBox1.Image);

Pen p=new Pen(Color.Black,5);
g.DrawLine(p,0,0,50,100);        //这里可以画你的第二幅图片
pictureBox1.Refresh();
pictureBox1.Image.Save(@"E:\123.bmp");