png图片(有含有透明)在IE6中为什么不透明了

png-8模式的图片，如果没有渐变的话是透明的，如果有渐变就不透明了。需要js的支持。

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=\"" + "" + 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);