function popup(url,titre,w,h)
{
  var left = (screen.width-w)/2;
  var top = (screen.height-h)/2;
  if (left < 0) left = 0;
  if (top < 0) top = 0;
  newwindow = window.open(url, titre, 'toolbar=no, location=no, directories=no, status=no, scrollbars=0, resizable=no, copyhistory=no, width=' + w + ', height=' + h + ', left=' + left + ', top='+ top +'');
  if (window.focus) {newwindow.focus()}
}