// <a href="html-or.jpg" onclick="return popup(this,123,456)" title="..."
// or
// <a href="html-or.jpg" onclick="return popup(this)" title="..."

var pop = null;

function popdown_skandic() {
  if (pop && !pop.closed) pop.close();
}

function popup_skandic(obj, w, h) {
  var url = (obj.getAttribute) ? obj.getAttribute('href') : obj.href;
  if (!url) return true;
  w = (w) ? w += 16 : 150;  // 150px*150px is the default size
  h = (h) ? h += 0 : 150;
  var screenw = screen.availWidth; 
  var screenh = screen.availHeight;
  var posx = (screenw / 2) - (w / 2); 
  var posy = ((screenh / 2) - (h / 2)) / 2
  var args = 'width='+w+',top='+posy+',left='+posx+',height='+h+',status=no,resizable, scrollbars, location=0';
  popdown_skandic();
  pop = window.open(url,'',args);
  return (pop) ? false : true;
}

window.onunload = popdown_skandic;
// window.onfocus = popdown_skandic;