C# winform 另存为picturebox里的图片

            saveFileDialog1.Filter = "JPeg Image|*.jpg|Bitmap Image|*.bmp|Gif Image|*.gif|PnG Image|*.png|Wmf  Image|*.wmf";
            saveFileDialog1.FilterIndex = 0;
            if (pictureBox1.Image == null)
            {
                MessageBox.Show("没有预览图片");
            }
            else if (saveFileDialog1.ShowDialog() == DialogResult.OK)
            {
                if (pictureBox1.Image != null)
                {
                    pictureBox1.Image.Save(saveFileDialog1.FileName, System.Drawing.Imaging.ImageFormat.Jpeg);
                }
            }