How to save bvh file using save file dialog?

private void button2_Click(object sender, System.EventArgs e)  
{  
   // Displays a SaveFileDialog so the user can save the Image  
   // assigned to Button2.  
   SaveFileDialog saveFileDialog1 = new SaveFileDialog();  
   saveFileDialog1.Filter = "JPeg Image|*.jpg|Bitmap Image|*.bmp|Gif Image|*.gif";  
   saveFileDialog1.Title = "Save an Image File";  
   saveFileDialog1.ShowDialog();  

   // If the file name is not an empty string open it for saving.  
   if(saveFileDialog1.FileName != "")  
   {  
      // Saves the Image via a FileStream created by the OpenFile method.  
      System.IO.FileStream fs =   
         (System.IO.FileStream)saveFileDialog1.OpenFile();  
      // Saves the Image in the appropriate ImageFormat based upon the  
      // File type selected in the dialog box.  
      // NOTE that the FilterIndex property is one-based.  
      switch(saveFileDialog1.FilterIndex)  
      {  
         case 1 :   
         this.button2.Image.Save(fs,   
            System.Drawing.Imaging.ImageFormat.Jpeg);  
         break;  

         case 2 :   
         this.button2.Image.Save(fs,   
            System.Drawing.Imaging.ImageFormat.Bmp);  
         break;  

         case 3 :   
         this.button2.Image.Save(fs,   
            System.Drawing.Imaging.ImageFormat.Gif);  
         break;  
      }  

   fs.Close();  
   }  
}