ie png图片显示不正常

png图片有很好的品质。阴影效果也不会有杂边,很流畅。如果插入网页的话可以给网站内容增色不少!更重要的是在不增加图片容量大小的情况下提高了页面的图片的质量。对于有复杂背景，如：在有颜色过度背景上插入不规则边框的图片带来极大很便利!

　　但目前IE中对于插入的透明背景的.png的图片是不能正常显示的。IE会自动给".png"格式的图片加个灰色背景。

　　解决这个的方法是增加javascript。具体方法如下：

　　把下面的代码放在head区就可以解决问题了。

我测试发现IE7.0可以正常显示出来，IE6及IE6以下不可以。

以下是引用片段：
<script language="javascript">
function correctPNG()
{
for(var i=0; i<document.images.length; i++)
{
var img = document.images[i]
var imgName = img.src.toUpperCase()
if (imgName.substring(imgName.length-3, imgName.length) == "PNG")

//这里不是很好，因为图片的格式不是由扩展名决定的，这里可以由server的方法去得到image真正的format传过来检查
{
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
i = i-1
}
}
}
window.attachEvent("onload", correctPNG);
</script>

　　也可以把这段代码单独加在一张图片上：

<!--<span
style="filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='testpng.png',sizingMethod='scale');"></span> -->

<IMG alt="" src="testpng.png">

------------------------------------------------------------------------------------------------------

PNG.JS代码：
// PNGHandler: Object-Oriented Javascript-based PNG wrapper
// --------------------------------------------------------
// Version 1.1.20031218
// Code by Scott Schiller - www.schillmania.com
// --------------------------------------------------------
// Description:
// Provides gracefully-degrading PNG functionality where
// PNG is supported natively or via filters (Damn you, IE!)
// Should work with PNGs as images and DIV background images.

function PNGHandler() {
var self = this;

this.na = navigator.appName.toLowerCase();
this.nv = navigator.appVersion.toLowerCase();
this.isIE = this.na.indexOf('internet explorer')+1?1:0;
this.isWin = this.nv.indexOf('windows')+1?1:0;
this.ver = this.isIE?parseFloat(this.nv.split('msie ')[1]):parseFloat(this.nv);
this.isMac = this.nv.indexOf('mac')+1?1:0;
this.isOpera = (navigator.userAgent.toLowerCase().indexOf('opera ')+1 || navigator.userAgent.toLowerCase().indexOf('opera/')+1);
if (this.isOpera) this.isIE = false; // Opera filter catch (which is sneaky, pretending to be IE by default)

this.transform = null;

this.getElementsByClassName = function(className,oParent) {
doc = (oParent||document);
matches = [];
nodes = doc.all||doc.getElementsByTagName('*');
for (i=0; i<nodes.length; i++) {
if (nodes[i].className == className || nodes[i].className.indexOf(className)+1 || nodes[i].className.indexOf(className+' ')+1 || nodes[i].className.indexOf(' '+className)+1) {
matches[matches.length] = nodes[i];
}
}
return matches; // kids, don't play with fire. ;)
}

this.filterMethod = function(oOld) {
// IE 5.5+ proprietary filter garbage (boo!)
// Create new element based on old one. Doesn't seem to render properly otherwise (due to filter?)
// use proprietary "currentStyle" object, so rules inherited via CSS are picked up.

var o = document.createElement('div'); // oOld.nodeName
var filterID = 'DXImageTransform.Microsoft.AlphaImageLoader';
// o.style.width = oOld.currentStyle.width;
// o.style.height = oOld.currentStyle.height;

if (oOld.nodeName == 'DIV') {
var b = oOld.currentStyle.backgroundImage.toString(); // parse out background image URL
oOld.style.backgroundImage = 'none';
// Parse out background image URL from currentStyle object.
var i1 = b.indexOf('url("')+5;
var newSrc = b.substr(i1,b.length-i1-2).replace('.gif','.png'); // find first instance of ") after (", chop from string
o = oOld;
o.style.writingMode = 'lr-tb'; // Has to be applied so filter "has layout" and is displayed. Seriously. Refer to http://msdn.microsoft.com/workshop/author/filter/reference/filters/alphaimageloader.asp?frame=true
o.style.filter = "progid:"+filterID+"(src='"+newSrc+"',sizingMethod='crop')";
// Replace the old (existing) with the new (just created) element.
// oOld.parentNode.replaceChild(o,oOld);
} else if (oOld.nodeName == 'IMG') {
var newSrc = oOld.getAttribute('src').replace('.gif','.png');
// apply filter
oOld.src = 'none.gif'; // get rid of image
oOld.style.filter = "progid:"+filterID+"(src='"+newSrc+"',sizingMethod='crop')";
oOld.style.writingMode = 'lr-tb'; // Has to be applied so filter "has layout" and is displayed. Seriously. Refer to http://msdn.microsoft.com/workshop/author/filter/reference/filters/alphaimageloader.asp?frame=true
}
}

this.pngMethod = function(o) {
// Native transparency support. Easy to implement. (woo!)
bgImage = this.getBackgroundImage(o);
if (bgImage) {
// set background image, replacing .gif
o.style.backgroundImage = 'url('+bgImage.replace('.gif','.png')+')';
} else if (o.nodeName == 'IMG') {
o.src = o.src.replace('.gif','.png');
} else if (!this.isMac) {
// window.status = 'PNGHandler.applyPNG(): Node is not a DIV or IMG.';
}
}

this.getBackgroundImage = function(o) {
var b, i1; // background-related variables
var bgUrl = null;

if (o.nodeName == 'DIV' && !(this.isIE && this.isMac)) { // ie:mac PNG support broken for DIVs with PNG backgrounds
if (document.defaultView) {
if (document.defaultView.getComputedStyle) {
b = document.defaultView.getComputedStyle(o,'').getPropertyValue('background-image');
i1 = b.indexOf('url(')+4;
bgUrl = b.substr(i1,b.length-i1-1);
} else {
// no computed style
}
} else {
// no default view
}
}
return bgUrl;
}

this.supportTest = function() {
// Determine method to use.
// IE 5.5+/win32: filter

if (this.isIE && this.isWin && this.ver >= 5.5) {
// IE proprietary filter method (via DXFilter)
self.transform = self.filterMethod;
} else if (!this.isIE && this.ver < 5) {
self.transform = null;
// No PNG support or broken support
// Leave existing content as-is
} else if (!this.isIE && this.ver >= 5 || (this.isIE && this.isMac && this.ver >= 5)) { // version 5+ browser (not IE), or IE:mac 5+
self.transform = self.pngMethod;
} else {
// Presumably no PNG support. GIF used instead.
self.transform = null;
return false;
}
return true;
}

this.init = function() {
if (this.supportTest()) {
this.elements = this.getElementsByClassName('png');
for (var i=0; i<this.elements.length; i++) {
this.transform(this.elements[i]);
}
}
}

}

// Instantiate and initialize PNG Handler

var pngHandler = new PNGHandler();

DEMO页HTML代码：
<html>
<head>
<title>Schillmania! | png.js demo</title>
<script type="text/javascript" src="png.js"></script>
</head>

<body>

<!--

Don't copy this part here, this is just for your information.

// Required under the <head> tag:

<script type="text/javascript" src="png.js"></script>

// Required in the <body> tag:

<img src="your-image.gif" class="png" style="width:XXXpx;height:YYYpx" />

// ..Where XXX and YYY are the width/height of your image. Without width/height the PNG won't work under IE:win32.

// Required before the </body> tag (but after all of your content):

<script type="text/javascript">
pngHandler.init();
</script>

// This javascript block should be put at the bottom of your page, inside the <body> and before </body>.
// It calls the library and replaces the GIF images (if applicable) before the page has loaded (and before the GIF has loaded, So the user doesn't load 2 images for each PNG you want to replace.)
// If you don't put it after all of your content, it may do strange things and miss some images.

-->

<h1>PNG (img)</h1>

<img src="foo.gif" alt="" class="png" style="width:220px;height:100px" />

<h1>PNG (div with background image)</h1>

<div class="png" style="width:220px;height:100px;background-image:url(foo.gif);background-repeat:no-repeat">

</div>

<script type="text/javascript">
pngHandler.init();
</script>

</body>
</html>

源码及DEMO打包下载：
详细出处参考：http://www.jb51.net/article/11196.htm