C#做绘图软件时怎样保存PictureBox中用graphics画的图

Graphics.FromImage(pictureBox1.Image).DrawEllipse(new Pen(Brushes.Red), e.X, e.Y, 1, 1);

            pictureBox1.Invalidate();

或者

 Graphics g = Graphics.FromImage(pictureBox1.Image); 

                    g.DrawRectangle(new Pen(Color.Red, 2), leftEgdeOfRetina, topEdgeOfRetina, rightEdgeOfRetina - leftEgdeOfRetina, bottomEdgeOfRetina - topEdgeOfRetina);

            pictureBox1.Invalidate();