window.addEvent('load', function() {

    var bgImg = $('background');
    bgImg.addClass('fullBg');

    function resizeImg() {
    	var imgwidth = bgImg.getSize().x;
    	var imgheight = bgImg.getSize().y;
        var winwidth = $(window).getSize().x;
        var winheight = $(window).getSize().y;
        var widthratio = winwidth / imgwidth;
        var heightratio = winheight / imgheight;
        var widthdiff = heightratio * imgwidth;
        var heightdiff = widthratio * imgheight;
        if (heightdiff > winheight) {
        	bgImg.setStyle('width',winwidth + 'px');
        	bgImg.setStyle('height',heightdiff + 'px');
        } else {
        	bgImg.setStyle('width',widthdiff + 'px');
        	bgImg.setStyle('height',winheight + 'px');
        }

    }
    resizeImg();
    window.addEvent('resize', function() {
        resizeImg();
    });
});