function ImageExpander(oThumb, sImgSrc) {
    // store thumbnail image and overwrite its onclick handler.
    this.oThumb = oThumb;
    this.oThumb.expander = this;
    this.oThumb.onclick = function() { this.expander.expand(); }

    // record original size
    this.smallWidth = oThumb.offsetWidth;
    this.smallHeight = oThumb.offsetHeight;

    // initial settings
    this.bExpand = true;
    this.bTicks = false;

    // insert into self organized list
    if (!window.aImageExpanders)
        window.aImageExpanders = new Array();
    window.aImageExpanders.push(this);

    // create the full sized image and automatically expand when loaded
    this.oImg = new Image();
    this.oImg.expander = this;
    this.oImg.onload = function() { this.expander.onload(); }
    this.oImg.src = sImgSrc;
}

ImageExpander.prototype.onload = function() {
    this.oDiv = document.createElement("div");
    document.body.appendChild(this.oDiv);
    this.oDiv.appendChild(this.oImg);
    this.oDiv.style.position = "absolute";
    this.oDiv.expander = this;
    this.oDiv.onclick = function() { this.expander.toggle(); };
    this.oImg.title = "";
    this.bigWidth = this.oImg.width;
    this.bigHeight = this.oImg.height;

    if (this.bExpand) {
        this.expand();
    }
    else {
        this.oDiv.style.visibility = "hidden";
        this.oImg.style.visibility = "hidden";
    }
}

ImageExpander.prototype.toggle = function() {
    this.bExpand = !this.bExpand;
    if (this.bExpand) {
        for (var i in window.aImageExpanders)
            if (window.aImageExpanders[i] !== this)
            window.aImageExpanders[i].reduce();
    }
}

ImageExpander.prototype.expand = function() {
    // set direction of expansion.
    this.bExpand = true;

    // set all other images to reduce
    for (var i in window.aImageExpanders)
        if (window.aImageExpanders[i] !== this)
        window.aImageExpanders[i].reduce();

    // if not loaded, don't continue just yet
    if (!this.oDiv)
        return;

    // hide the thumbnail
    this.oThumb.style.visibility = "hidden";

    // calculate initial dimensions
    this.x = this.oThumb.offsetLeft;
    this.y = this.oThumb.offsetTop;
    this.w = this.oThumb.clientWidth;
    this.h = this.oThumb.clientHeight;

    this.oDiv.style.left = this.x + "px";
    this.oDiv.style.top = this.y + "px";
    this.oImg.style.width = this.w + "px";
    this.oImg.style.height = this.h + "px";
    this.oDiv.style.visibility = "visible";
    this.oImg.style.visibility = "visible";

    // start the animation engine.
    if (!this.bTicks) {
        this.bTicks = true;
        var pThis = this;
        window.setTimeout(function() { pThis.tick(); }, 25);
    }
}

ImageExpander.prototype.reduce = function() {
    // set direction of expansion.
    this.bExpand = false;
}

ImageExpander.prototype.tick = function() {
    // calculate screen dimensions
    var cw = document.body.clientWidth;
    var ch = document.body.clientHeight;
    var cx = document.body.scrollLeft + cw / 2;
    var cy = document.body.scrollTop + ch / 2;

    // calculate target
    var tw, th, tx, ty;
    if (this.bExpand) {
        // start with the full size dimensions
        tw = this.bigWidth;
        th = this.bigHeight;

        // reduce to fit the screen
        if (tw > cw) {
            th *= cw / tw;
            tw = cw;
        }
        if (th > ch) {
            tw *= ch / th;
            th = ch;
        }

        // then center it on the page
        tx = cx - tw / 2;
        ty = cy - th / 2;
    }
    else {
        tw = this.smallWidth;
        th = this.smallHeight;
        tx = this.oThumb.offsetLeft;
        ty = this.oThumb.offsetTop;
    }

    // move 10% closer to target
    var nHit = 0;
    var fMove = function(n, tn) {
        var dn = tn - n;
        if (Math.abs(dn) < 3) {
            nHit++;
            return tn;
        }
        else {
            return n + dn / 10;
        }
    }
    this.x = fMove(this.x, tx);
    this.y = fMove(this.y, ty);
    this.w = fMove(this.w, tw);
    this.h = fMove(this.h, th);

    this.oDiv.style.left = this.x + "px";
    this.oDiv.style.top = this.y + "px";
    this.oImg.style.width = this.w + "px";
    this.oImg.style.height = this.h + "px";

    // if reducing and size/position is a match, stop the tick   
    if (!this.bExpand && (nHit == 4)) {
        this.oImg.style.visibility = "hidden";
        this.oDiv.style.visibility = "hidden";
        this.oThumb.style.visibility = "visible";

        this.bTicks = false;
    }

    if (this.bTicks) {
        var pThis = this;
        window.setTimeout(function() { pThis.tick(); }, 25);
    }
}