var bgImgNr = Math.floor(Math.random() * 4);
function switchBackgroundImage(){
	var imgArr = new Array("bg_subheader_01.jpg", "bg_subheader_02.jpg", "bg_subheader_03.jpg", "bg_subheader_04.jpg");
	++bgImgNr;
	var currentImgNr = (bgImgNr%imgArr.length);
	var imgName = imgArr[currentImgNr];
	var newImgUrl = "url(fileadmin/templates/images/subheader/"+imgName+")";
	$('slideshow').style.backgroundImage = newImgUrl;
	new Effect.Opacity('ch_transition', {
		duration:2,
		from:1.0,
		to:0.0,
		afterFinish: function () {
			$('ch_transition').style.backgroundImage = newImgUrl;
			new Effect.Opacity('ch_transition', {	
				duration:0.5,
				from:0.0,
				to:1.0
			});
		}
	});

}
Event.observe(window, 'load', function() {
	switchBackgroundImage();
	new PeriodicalExecuter(switchBackgroundImage, 7);
});