window.onresize = function (){
	var ratio = 1200/800;
	
	if( document.viewport.getWidth() / document.viewport.getHeight() > ratio){
	    $$('#bg img').each(function(el){ el.setStyle({height: 'auto', width: '100%', display:'block'}) } );
	}else{
		$$('#bg img').each(function(el){ el.setStyle({width: 'auto', height: '100%', display:'block'}) } );
	}

};