function popup_pics (url, w, h)
{
  var x = (screen.availwidth-w)/2,
      y = (screen.availheight-h)/2;
  window.open(url, 'popup_image', 'width='+w+',height='+h+',left='+x+',top='+y+',menubar=no,scrollbars=no,status=no,toolbar=no');
  return false;
}