pictruebox 画了一条直线，保存无效问题

       private void save_Click(object sender, EventArgs e)     // 保存功能，不报错，但是不能显示图片
        {
            SaveFileDialog saveFileDialog1 = new SaveFileDialog();
            saveFileDialog1.FileName = "未命名";
            saveFileDialog1.Filter = "jpg图片(*.jpg)|*.jpg|位图文件|*.bmp|所有文件|*.*";

            if (saveFileDialog1.ShowDialog() == DialogResult.OK)
            {
                if (pictureBox1.Image == null) return;
                pictureBox1.Image.Save(saveFileDialog1.FileName);

            }

        }