var newWin= null;
function popUp (img) {
  mypage = "popkep.php?img=" + img;
  w = 500;
  h = 500;
  onfocus = function() {
    if(!newWin.closed) newWin.close();
  }
  var winl = (screen.width-w)/2;
  var wint = (screen.height-h)/2 - 100;
  var settings  ='height='+h+',';
      settings +='width='+w+',';
      settings +='top='+wint+',';
      settings +='left='+winl+',';
      settings +='scrollbars=no,';
      settings +='resizable=yes';
  newWin = window.open(mypage, "mywin", settings);
  if(parseInt(navigator.appVersion) >= 4){newWin.window.focus();}
}