WEB关于鼠标滑过变化图片的函数swapImage中怎么调整切换图片的透明度问题

这是body部分

 <a  href="javascript:show()" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('Image12','','image/双子座.png',1)" ><img  src="image/双子座1.jpg" width="306" height="402" id="Image12" /></a>

这是

 <script>
function MM_swapImage() { //v3.0
  var i,j=0,x,a=MM_swapImage.arguments; document.MM_sr=new Array; for(i=0;i<(a.length-2);i+=3)
   if ((x=MM_findObj(a[i]))!=null){document.MM_sr[j++]=x; if(!x.oSrc) x.oSrc=x.src; x.src=a[i+2];}
}

自己找效果，dw默认的切换没有淡入淡出功能
http://www.jbxue.com/article/js/21796.html
http://blog.csdn.net/aloie/article/details/2840845