Как сохранить картинку?

private: System::Void bnt_save_graphics_Click(System::Object^  sender, System::EventArgs^  e) 
         {  
    
      SaveFileDialog ^ saveFileDialog1 = gcnew SaveFileDialog();
      saveFileDialog1->Filter =  "JPeg Image|*.jpg|Bitmap Image|*.bmp|Gif Image|*.gif";
      saveFileDialog1->Title = "Save an Image File";
      saveFileDialog1->ShowDialog();
      Bitmap ^bm = gcnew Bitmap(picBox1->Width, picBox1->Height);
             Graphics ^Image = Graphics::FromImage(bm);
             Image->DrawLines(Pens::Blue, pointsScreen);
          bm->Save("testImage.bmp");
      if(saveFileDialog1->FileName != "")
      {
      
         System::IO::FileStream ^ fs = safe_cast<System::IO::FileStream^>(saveFileDialog1->OpenFile());
     
         switch(saveFileDialog1->FilterIndex)
         { 
            case 1 :
               this->bnt_save_graphics->Image->Save(fs, System::Drawing::Imaging::ImageFormat::Jpeg);
               break;
            case 2 :
               this->bnt_save_graphics->Image->Save(fs, System::Drawing::Imaging::ImageFormat::Bmp);
               break;
            case 3 :
               this->bnt_save_graphics->Image->Save(fs, System::Drawing::Imaging::ImageFormat::Gif);
               break;
         }
      fs->Close();
      }
   }

if( saveFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK )
{
        // сохранение и т.д....
        // например:
        pictureBox1->Image->Save( saveFileDialog1->FileName,Imaging::ImageFormat::Bmp );
}