Add smoothness between changing images with jQuery
<p>I have this code that changes the image when a user rolls over a map area on my United States map. It is working perfectly. But I want the the images to have a smooth appearance and then a gradual fade away. What do I need to add to this code? Thanks! </p>

<pre><code>$(document).ready(function() {

//set off state 
var nav_off = "/images/state-map.png";

// functions for over and off
function over(image) {
    $("#main-nav").attr("src", image);
}
function off() {
    $("#main-nav").attr("src", nav_off);
}

$("#imagemap area").hover(
    function () {
        var button = $(this).attr("id");
        over("/images/state-" + button + ".png");
    },
    function () {
        off();
    });

});
</code></pre>
