图片交替渐变出现的效果实现

http://my.oschina.net/HeYuhui/blog/632467

function change2(){
    document.getElementById("img2").style.zIndex='2';
    document.getElementById("img1").style.zIndex='1';
    document.getElementById("img1").style.opacity='1';
    $("#img2").animate({opacity:'0'},2000);
        }
function change3(){
    document.getElementById("img1").style.zIndex='2';
    document.getElementById("img2").style.zIndex='1';
    $("#img1").animate({opacity:'0'},2000);
    document.getElementById("img2").style.opacity='1';
        }
function change4(){
            setTimeout("change2()",5000);
            setTimeout("change3()",12000);
            setTimeout("change4()",14000);
        }