public void Close()
 {
     if (_form != null)
     {
         _form.Dispose();
         _form = null;
     }
 }
 public void Open(IPresentationImage image, Point locationTile, RenderMagnifiedImage render)
 {
     _form = new MagnificationForm((PresentationImage)image, locationTile, render);
     _form.Show();
 }