function stretchBG() {
    var pageHeight = $(document).height();
    var viewportHeight = $(window).height();

    var bgrdDiv = document.getElementById("babkgroundImg");

    if (bgrdDiv != null) {
        if (pageHeight > viewportHeight) {
            bgrdDiv.style.height = pageHeight + "px";
        }
        else {
            bgrdDiv.style.height = viewportHeight + "px";
        }
    }
}

$(document).ready(function() {
    stretchBG();
});