function Obj(lgh,imgname,directory,add){
	if(!document.images) return;
	var dir=directory+'images/'+imgname;
	this.imgname=imgname;
	this.lgh=lgh;
	this.images=new Array(lgh);
	for(var i=0; i < lgh; i++){
		this.images[i]=new Object();
		this.images[i].on=new Image();
		this.images[i].off=new Image();
		this.images[i].on.src=dir+(i+1)+'_on.'+add;
		this.images[i].off.src=dir+(i+1)+'_off.'+add;
	}
	return this;
}
new Obj(0,'','',''); //for N2,N3
Obj.prototype.rollon=Obj_rollon;
Obj.prototype.rolloff=Obj_rolloff;
function Obj_rollon(n){
	if(!document.images) return false;
	else document[this.imgname+n].src=this.images[n-1].on.src;
}
function Obj_rolloff(n){
	if(!document.images) return false;
	else document[this.imgname+n].src=this.images[n-1].off.src;
}