window.addEvent('domready', function(){
    bg();

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

function bg(){
    var windowxsize = window.getSize().x;
    var windowysize = window.getSize().y;
    var imgxsize = 1024;
    var imgysize = 773;
    

    if((windowxsize/imgxsize*imgysize)>windowysize)
    {
    var vsize = windowxsize/imgxsize*imgysize;
    var hsize = windowxsize;
    
    $('bg_img').setStyle('height',vsize);
    $('bg_img').setStyle('width',hsize);    
    }
    
    if((windowxsize/imgxsize*imgysize)<=windowysize)
    {
    var vsize = windowysize;

    var hsize = windowysize/imgysize*imgxsize;
    $('bg_img').setStyle('height',vsize);
    $('bg_img').setStyle('width',hsize);    
    }
}