对class="imgBox"的元素内的图片自动等比例缩小，本例放在ul中，利用li可以让图片有边框和背景色
图片自动等比例缩小，其实如果不考虑ie6的话，用css就可以实现，设定img的max-width和max-height，而<img>标签内不设定widht和height即可。
ie7已经支持max-width和max-height，这是为数不多的好消息之一。
但是对于ie6及以前的版本，就只能用js来设置了。
在 ff 2.0 / ie6 / ie7 / op 8.5+ / sa 3 中测试通过。
不过垂直方向在 ff 和 sa 中稍微有些错位，还需解决。
希望大家来测试找bug
注意：垂直居中的关键在于文档的dtd类型！！
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh-cn" lang="zh-cn">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>图片自动等比例缩小且垂直居中</title>
<!--[if lte IE 6]>
<script type="text/javascript" language="javascript">
function imgFix() {
//定义要限制的图片宽高,这个宽高要同style里面定义的相同，小于限定高宽的图片不操作
var widthRestriction = 200;
var heightRestriction = 200;
var allElements = document.getElementsByTagName('*')
for (var i = 0; i < allElements.length; i++)
{
if (allElements[i].className.indexOf('imgBox') >= 0)
{
var imgElements = allElements[i].getElementsByTagName('img');
for (var j=0; j < imgElements.length; j++)
{
if ( imgElements[j].width > widthRestriction || imgElements[j].height > heightRestriction )
{
if ( imgElements[j].width > imgElements[j].height)
{
imgElements[j].height = imgElements[j].height*(widthRestriction/imgElements[j].width);
imgElements[j].width = widthRestriction;
} else
{
imgElements[j].width = imgElements[j].width*(heightRestriction/imgElements[j].height);
imgElements[j].height = heightRestriction;
}
}
if ( imgElements[j].height < heightRestriction )
{
imgElements[j].style.paddingTop = ( heightRestriction -imgElements[j].height ) /2 + "px";
}
} /*for j*/
}
}/*for i*/
}
window.onload = imgFix;
</script>
<![endif]-->
<style type="text/css">
<!--
* {
margin:0;
padding:0;
}
body {
font: 8px/1em serif; /* 字号会影响图片的垂直位置 */
}
.imgBox li {
list-style:none;
width:200px; /* 宽度 */
height:200px; /* 高度 */
background:#ccc;
border:1px solid #666;
text-align:center;
margin:5px;
line-height:200px;
}
.imgBox img {
max-width:200px; /* 宽度 */
max-height:200px; /* 高度 */
vertical-align:middle;
}
-->
</style>
</head>
<body>
<ul class="imgBox">
<li><img src="http://www.ddcat.net/tebie/coco/img/coco_20070618_03.jpg" alt="img" /></li>
<li><img src="http://www.ddcat.net/tebie/coco/img/coco_20070618_04.jpg" alt="img" /></li>
<li><img src="http://www.ddcat.net/bbs2007/images/style_1/zh-cn/redirect_logo.gif" alt="img" /></li>
<li><img src="http://www.ddcat.net/blog/templates/ddcat2007/img/logo.gif" alt="img" /></li>
</ul>
</body>
</html>
同时加载多个方法
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>图片自动等比例缩小且垂直居中</title>
<script type="text/javascript" language="javascript">
function imgFix(selector, width, height) {
function hasClass(selector, thisClass){
var classes = thisClass.split(" ");
for (var i=0;i<classes.length;++i) {
if (classes[i] == selector) {
return true;
}
}
return false;
};
//定义要限制的图片宽高,这个宽高要同style里面定义的相同，小于限定高宽的图片不操作
//alert(selector);
var widthRestriction = width;
var heightRestriction = height;
var allElements = document.getElementsByTagName('*');
for (var i = 0; i < allElements.length; i++) {
//if (allElements[i].className.indexOf(selector) >= 0) {
if (hasClass(selector, allElements[i].className)) {
var imgElements = allElements[i].getElementsByTagName('img');
for (var j=0; j < imgElements.length; j++) {
if ( imgElements[j].width > widthRestriction || imgElements[j].height > heightRestriction ) {
if ( imgElements[j].width > imgElements[j].height) {
imgElements[j].height = imgElements[j].height*(widthRestriction/imgElements[j].width);
imgElements[j].width = widthRestriction;
}
else {
imgElements[j].width = imgElements[j].width*(heightRestriction/imgElements[j].height);
imgElements[j].height = heightRestriction;
}
}
if ( imgElements[j].height < heightRestriction ) {
imgElements[j].style.paddingTop = ( heightRestriction -imgElements[j].height ) /2 + "px";
}
} /*for j*/
}
} /*for i*/
}
window.onload = function(){
imgFix("imgBox", 200, 200);
imgFix("imgBox2", 300, 300);
imgFix("imgBox3", 400, 400);
};
</script>
<style type="text/css">
* {
margin:0;
padding:0;
}
img{ border:none;}
.imgBox li {list-style:none;width:200px;height:200px; background:#ccc; border:1px solid #666;text-align:center; margin-left:10px; padding:2px; margin-top:5px; overflow:hidden;}
.imgBox img { max-width:200px max-height:200px;vertical-align:middle;}
.imgBox2 li {list-style:none;width:300px;height:300px; background:#ccc; border:1px solid #666;text-align:center; margin-left:10px; padding:2px; margin-top:5px; }
.imgBox2 img { max-width:300px; max-height:300px;vertical-align:middle;}
.imgBox3 li {list-style:none;width:400px;height:400px; background:#ccc; border:1px solid #666;text-align:center; margin-left:10px; padding:2px; margin-top:5px; }
.imgBox3 img { max-width:400px; max-height:400px;vertical-align:middle;}
</style>
</head>
<body>
<ul class="imgBox">
<li><a href="#"><img src="01.jpg" alt="img" /></a></li>
<li><a href="#"><img src="03.jpg" alt="img" /></a></li>
<li><a href="#"><img src="02.jpg" alt="img" /></a></li>
</ul>
<ul class="imgBox2">
<li><a href="#"><img src="01.jpg" alt="img" /></a></li>
<li><a href="#"><img src="03.jpg" alt="img" /></a></li>
<li><a href="#"><img src="02.jpg" alt="img" /></a></li>
</ul>
<ul class="imgBox3">
<li><a href="#"><img src="01.jpg" alt="img" /></a></li>
<li><a href="#"><img src="111.jpg" alt="img" /></a></li>
<li><a href="#"><img src="02.jpg" alt="img" /></a></li>
</ul>
</body>
</html>