关于图片无缝滚动抖动问题

滚dog一排没事，但是滚动多几排就抖了，怎么解决啊？<div id="gd1" style="overflow:hidden;width:970px;">
<table cellpadding="0" cellspacing="0" border="0">
<tr><td id="gd2" valign="top" align="center">
<table cellpadding="2" cellspacing="0" border="0">
<tr align="center">
<td>内容</td>
</tr>
</table>
</td>
<td id="gd3" valign="top"></td>
</tr>
</table>
</div>
<script>
var speed=31//速度数值越大速度越慢
var gd3=document.getElementById("gd3");
var gd2=document.getElementById("gd2");
var gd1=document.getElementById("gd1");
gd3.innerHTML=gd2.innerHTML
function Marquee1(){
if(gd1.scrollLeft<=0)
gd1.scrollLeft+=gd3.offsetWidth
else{
gd1.scrollLeft--
}
}
var MyMar1=setInterval(Marquee1,speed)
gd1.onmouseover=function() {clearInterval(MyMar1)}
gd1.onmouseout=function() {MyMar1=setInterval(Marquee1,speed)}
</script>这是代码
<div id="gd4" style="overflow:hidden;width:970px;">
<table cellpadding="0" cellspacing="0" border="0">
<tr><td id="gd5" valign="top" align="center">
<table cellpadding="2" cellspacing="0" border="0">
<tr align="center">
<td>内容</td>
</tr>
</table>
</td>
<td id="gd6" valign="top"></td>
</tr>
</table>
</div>
<script>
var speed=32//速度数值越大速度越慢
var gd6=document.getElementById("gd6");
var gd5=document.getElementById("gd5");
var gd4=document.getElementById("gd4");
gd6.innerHTML=gd5.innerHTML
function Marquee2(){
if(gd4.scrollLeft<=0)
gd4.scrollLeft+=gd6.offsetWidth
else{
gd4.scrollLeft--
}
}
var MyMar2=setInterval(Marquee2,speed)
gd4.onmouseover=function() {clearInterval(MyMar2)}
gd4.onmouseout=function() {MyMar2=setInterval(Marquee2,speed)}
</script>