function setImg(type) {
	obj=document.getElementById('bigImg');
	oSrc = obj.src;
	oId = oSrc.substring(oSrc.lastIndexOf('/')+1, oSrc.length-4);
	if ('left' == type) {
		nId = --oId;
	}
	else {
		nId = ++oId;
	}
	if (nId > 18) nId = 0;
	if (nId < 0) nId = 18
	img='./img/theater/'+nId+'.jpg'
	obj.src=img;
}