js png图片(有含有透明)在IE6中为什么不透明了

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);