<!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>无标题文档</title>
<style>
.sy_pic{ width:500px; height:300px; border:#000 solid 5px; text-align:center;}
</style>
<script type="text/javascript" language="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="bg.jpg" /></div>
</body>
</html>
