怎么把PICTUREBOX里的图片保存到本地？C#

private void button1_Click(object sender, EventArgs e)//保存图片
{
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 != "")
{
System.IO.FileStream fs = (System.IO.FileStream)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:

SaveFileDialog saveFileDialog = new SaveFileDialog();
saveFileDialog.Filter = "Image files (*.jpg)|*.jpg";
saveFileDialog.FilterIndex = 0;
saveFileDialog.RestoreDirectory = true;
saveFileDialog.Title = "导出文件保存路径";
saveFileDialog.FileName = null;
saveFileDialog.ShowDialog();
string strPath = saveFileDialog.FileName;

Image img = pictureBox1.Image;
img.Save(strPath);

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