window.addEvent('domready', function() {
	$$('img.roll').each(function(img) {
		var src = img.getProperty('src');
		var extension = src.substring(src.lastIndexOf('.'),src.length)
		img.addEvent('mouseenter', function() { img.setProperty('src',src.replace(extension,'_b' + extension)); });
		img.addEvent('mouseleave', function() { img.setProperty('src',src); });
	});
});