(function($) {
    $.fn.fullBg = function() {
        var bgImg = $(this);

        bgImg.addClass('fullBg');

        function resizeImg() {
            var imgwidth = bgImg.width();
            var imgheight = bgImg.height();

            var winwidth = $(window).width();
            var winheight = $(window).height();

            var widthratio = winwidth / imgwidth;
            var heightratio = winheight / imgheight;

            var widthdiff = heightratio * imgwidth;
            var heightdiff = widthratio * imgheight;

            if (heightdiff > winheight) {
                bgImg.css({
                    width: winwidth + 'px',
                    height: heightdiff + 'px'
                });
            } else {
                bgImg.css({
                    width: widthdiff + 'px',
                    height: winheight + 'px'
                });
            }
        }
        resizeImg();
        $(window).resize(function() {
            resizeImg();
        });
    };
})(jQuery)

jQuery(function($) {
    $("#background").fullBg();
});