ขอถามเรื่องการหน่วงเวลาให้ smooth ในการ hide และ show element หน่อยครับ

<script type='text/javascript'>
var slide={
	tmo:null,
	opa:100,
	duration:140,
	frame:8,
	process:false,
	active:function(a){
		if(this.process)return;
		if(a=='show') this.show();
		else this.hide();
	},
	show:function(){
		if(this.opa<100){
					this.process=true;
			this.opa+=100/this.frame;
			this.setOpacity(this.opa,'imgs');
			var _this =this;
		 	this.tmo=setTimeout(function(){_this.show()},this.duration);
		}else{
				this.setOpacity(100,'imgs');
			clearTimeout(this.tmo);
			this.process=false;

		}
	},
	hide:function(){
		if(this.opa>0){
					this.process=true;
			this.opa-=100/this.frame;
			this.setOpacity(this.opa,'imgs');
			var _this =this;
		 	this.tmo=setTimeout(function(){_this.hide()},this.duration);
		}else{
			clearTimeout(this.tmo);
			this.setOpacity(0,'imgs');
			this.process=false;
		}
	},
	setOpacity:function(setOpacity, objectId){
		var object = document.getElementById(objectId).style;	
		object.opacity = (setOpacity / 100);
		object.MozOpacity = (setOpacity / 100);
		object.KhtmlOpacity = (setOpacity / 100);
		object.filter = "alpha(opacity=" + setOpacity + ")";
		
	}
}
</script>
<img src='http://www.keedkean.com/images/upload/2/220100208104545.jpg' id='imgs'><br>
<input type='button' value='click to show' onclick="slide.active('show')"><input type='button' value='click to hide' onclick="slide.active('hide')">