<!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=utf-8" />
<title>By：DragonDean</title>
<style type="text/css">
.sy_pic{ width:200px; height:200px; text-align:center;}
</style>
<script type="text/javascript">
window.onload = function () {
changeImgSize();
}
function changeImgSize() {
var getContainer = document.getElementById(‘imgcontainer‘);
var getIMG = getContainer.getElementsByTagName(‘img‘)[0];
var fw = getContainer.offsetWidth - (2 * getContainer.clientLeft);
var fh = getContainer.offsetHeight - (2 * getContainer.clientTop);
var iw = getIMG.width;
var ih = getIMG.height;
var m = iw / fw;
var n = ih / fh;
if (m >= 1 && n <= 1) {
iw = Math.ceil(iw / m);
ih = Math.ceil(ih / m);
getIMG.width = iw;
getIMG.height = ih;
}
else if (m <= 1 && n >= 1) {
iw = Math.ceil(iw / n);
ih = Math.ceil(ih / n);
getIMG.width = iw;
getIMG.height = ih;
}
else if (m >= 1 && n >= 1) {
getMAX = Math.max(m, n);
iw = Math.ceil(iw / getMAX);
ih = Math.ceil(ih / getMAX);
getIMG.width = iw;
getIMG.height = ih;
}
if (getIMG.height < fh) {
var getDistance = Math.floor((fh - getIMG.height) / 2);
getIMG.style.marginTop = getDistance.toString() + "px";
}
}
</script>
</head>
<body>
<div class="sy_pic" id="imgcontainer"><img src="/images/test.jpg" /></div>
</body>
</html>
原文：http://www.cnblogs.com/dangzhenjiuhao/p/4824906.html