IE下png实现透明

<script language="JavaScript"> 
function correctPNG() // correctly handle PNG transparency in Win IE 5.5 & 6. 
{ 
    var arVersion = navigator.appVersion.split("MSIE") 
    var version = parseFloat(arVersion[1]) 
    if ((version >= 5.5) && (document.body.filters)) 
    { 
       for(var j=0; j<document.images.length; j++) 
       { 
          var img = document.images[j] 
          var imgName = img.src.toUpperCase() 
          if (imgName.substring(imgName.length-3, imgName.length) == "PNG") 
          { 
             var imgID = (img.id) ? "id='" + img.id + "' " : "" 
             var imgClass = (img.className) ? "class='" + img.className + "' " : "" 
             var imgTitle = (img.title) ? "title='" + img.title + "' " : "title='" + img.alt + "' " 
             var imgStyle = "display:inline-block;" + img.style.cssText 
             if (img.align == "left") imgStyle = "float:left;" + imgStyle 
             if (img.align == "right") imgStyle = "float:right;" + imgStyle 
             if (img.parentElement.href) imgStyle = "cursor:hand;" + imgStyle 
             var strNewHTML = "<span " + imgID + imgClass + imgTitle 
             + " style=\"" + "width:" + img.width + "px; height:" + img.height + "px;" + imgStyle + ";" 
             + "filter:progid:DXImageTransform.Microsoft.AlphaImageLoader" 
             + "(src=\'" + img.src + "\', sizingMethod='scale');\"></span>" 
             img.outerHTML = strNewHTML 
             j = j-1 
          } 
       } 
    }     
} 
window.attachEvent("onload", correctPNG); 
</script>