在picturebox绘图并保存的问题，下面是保存按钮的代码，不知哪里出问题了

private void button1_Click(object sender, EventArgs e)
        {
            saveFileDialog1.Filter = "JPeg Image|*.jpg|Bitmap Image|*.bmp|Gif Image|*.gif|PNG Image|*.png";
            saveFileDialog1.Title = "Save";
            saveFileDialog1.FileName = string.Empty;
            saveFileDialog1.ShowDialog();
            if (saveFileDialog1.FileName != "")
            {
                fs = ()saveFileDialog1.OpenFile();
                switch (saveFileDialog1.FilterIndex)
                {
                    case 1:
                        this.pictureBox1.Image.Save(fs, System.Drawing.Imaging.ImageFormat.Jpeg);
                        break;
                    case 2:
                        this.pictureBox1.Image.Save(fs, System.Drawing.Imaging.ImageFormat.Bmp);
                        break;
                    case 3:
                        this.pictureBox1.Image.Save(fs, System.Drawing.Imaging.ImageFormat.Gif);
                        break;
                    case 4:
                        this.pictureBox1.Image.Save(fs, System.Drawing.Imaging.ImageFormat.Png);
                        break;
                }
                fs.Close();
            }
        }