function imgAlpha() 
{
    // Funzione transizioni
    function fx(el, tmp, type) {el.set(type, {duration: tmp, transition: Fx.Transitions.linear})}    

    // Effetti rollover immagine
    var img = $$('a.rollover','div.rollover','img.rollover')
    img.set('opacity', 1)
    fx(img, 280, 'tween')
    
    img.addEvents({
        'mouseover': function(){
            this.tween('opacity', 0.5)
        },
        'mouseleave': function(){
            this.tween('opacity', 1)
        }
    })
}

window.addEvent('domready', imgAlpha)