DURATION = 10000;
TRANSITION = Fx.Transitions.Quad.easeOut

function swap_image(img, new_image_src) {
  var new_img = new Element("img", { src:new_image_src });
  img.alterego = new_img;
  new_img.original = img;
  new_img.setStyles({position:"absolute"});
  new_img.setOpacity(0);
  new_img.setStyles(img.getCoordinates());
  new_img.injectInside(img.getParent());
  start_cycle(img);
}

function start_cycle(img) {
  img.alterego.effects({duration: DURATION/2, transition:TRANSITION,
                        onComplete: function (i) { end_cycle(i)}}).start({opacity:[0,1]});
}

function end_cycle(new_img) {
  new_img.effects({duration: DURATION/2, transition:TRANSITION,
                   onComplete: function (i) { start_cycle(i.original)}}).start({opacity:[1,0]});
}

function init_logo() {
  swap_image($('logo'), "/media/img/logo-monthey.jpg");
}
window.addEvent("load", function () {
  init_logo.delay(1000);
});