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

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