function menu_brighten(n){
  brighten('menu-image-' + n);
  brighten('menu-text-' + n);
}
function menu_unbrighten(n){
  unbrighten('menu-image-' + n);
  unbrighten('menu-text-' + n);
}

function brighten(id){
  obj = $(id)
  if (!Object.isUndefined(obj)){
    obj.addClassName('opaque')
  }
}

function unbrighten(id){
  obj = $(id)
  if (!Object.isUndefined(obj)){
    obj.removeClassName('opaque')
  }
}