function fadeImages(id,nbTrans,delay) {     
var elm = document.getElementById(id).getElementsByTagName('img')[0]; // l element qui doit etre dégradé 
   elm.style.opacity = 1;   
   var interval;     
   elm.onmouseover = function() {
   if (interval) clearInterval(interval);makeTrans(1);}   
   elm.onmouseout = function() {
   if (interval) clearInterval(interval);makeTrans(0);}    

   function makeTrans(start) {       
   var opacity = start;     
   interval = setInterval(function() {     
   elm.style.filter = "alpha(opacity="+100*opacity+" )";    
   elm.style.opacity = opacity;       
   opacity += Math.pow(-start,start)/nbTrans;       
   if (opacity<0 || opacity>1) {    
   clearInterval(interval);           
   var end = start == 1 ? 0 :1         
   elm.style.filter = "alpha(opacity="+100*end+" )";      
   elm.style.opacity = end;            }        },delay);     
   }       
   } onload = function() {  
   fadeImages("logo",50,20);};