// Open preview
  function open_preview(url,width,height) {
   var left = (window.screen.width - width) / 1;
   var top = (window.screen.height - height) / 1;
   var parameters = 'left=' + left + ',top=' + top + ',width=' + width + ',height=' + height + ',toolbar=1,menubar=0,location=0,status=0,scrollbars=1,resizable=1';
   window.open(url,'preview',parameters);
  }