$(function() {   
		
			var theWindow        = $(window),
			    $bg              = $("#bg"),
			    aspectRatio      = $bg.width() / $bg.height();
			    			    		
			function resizeBg() {
				
				if ( (theWindow.width() / theWindow.height()) < aspectRatio ) {
				    $bg
				    	.removeClass()
				    	.addClass('bgheight');
				} else {
				    $bg
				    	.removeClass()
				    	.addClass('bgwidth');
				}
							
			}
			                   			
			theWindow.resize(function() {
				resizeBg();
			}).trigger("resize");
		
		});