Gallery problem

//JavaScript Document

function setOpacity(value) {
    var img = document.getElementById("lightBox");
    img.style.opacity = value/350;
    img.style.filter ="alpha(opacity=" + (value/2) + ")";
    if(value > 0 ) img.style.display = "block";
    if(value == 0) img.style.display = "none";
    var img = document.getElementById("lightBoxImg");
    img.style.opacity = value/350;
    img.style.filter ="alpha(opacity=" + value + ")";
}

function setSource(value, left, top) {
    var img = document.getElementById("lightBoxImg");
    img.src = value;
    img.style.marginLeft = left + "px";
    img.style.marginTop = top + "px";
}

var oc = 0;
var ocTarget = 0;

function animation() {
    if(oc > ocTarget) {
        oc--;
    }
    if(oc < ocTarget) {
        oc++;
    }
    setOpacity(oc);
}

setInterval(animation, 10);