如何让一张图片有浅到深的渐变

〈SCRIPT language=javascript1.2〉
〈!--
function high(which2){
theobject=which2
highlighting=setInterval(highlightit(theobject),50)
}
function low(which2){
clearInterval(highlighting)
which2.filters.alpha.opacity=40
}
function highlightit(cur2){
if (cur2.filters.alpha.opacity〈100)
cur2.filters.alpha.opacity+=10
else if (window.highlighting)
clearInterval(highlighting)
}
〈/script〉
〈img onmouseout=low(this) onmouseover=high(this