Bitmap bmp = new Bitmap(backgroundImage_.Width, backgroundImage_.Height, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
using (Graphics g = Graphics.FromImage(bmp))
{
     g.DrawImage(backgroundImage_, new Point(0, 0));
}
bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
bmp.Dispose();