<!DOCTYPE html>
<html>
<head>
<meta charset="gb2312">
<title>图片中心点全屏缩放代码</title>
<script type="text/javascript" src="http://i1.sinaimg.cn/jslib/jquery-1.4.2.min.js"></script>
<style>
body {padding:0; margin:0;}
#coverpage{ width: 100%; height: 100%; z-index: 9999; background: #000; overflow: hidden; position: absolute;}
#onepics{ width: 100%; height: 100%; overflow: hidden; position: relative;}
.onepic_wrap{ width: 100%; height: 100%; overflow: hidden; display: block; position: relative; cursor: pointer;}
.onepic_bg{ position: absolute; left: 0; bottom: 0; height: 45px;width: 100%;color:#fff;background:rgba(0,0,0, 0.5); filter:progid:DXImageTransform.Microsoft.Gradient(GradientType=0, StartColorStr=‘#7f000000‘, EndColorStr=‘#7f000000‘);*zoom:1;}
:root .onepic_bg{filter:progid:DXImageTransform.Microsoft.Gradient(GradientType=0, StartColorStr=‘#00000000‘, EndColorStr=‘#00000000‘); }
.onepic_bg p{ height: 45px; line-height: 45px; padding-left: 95px; font-size: 13px; color: #fff; text-overflow:ellipsis; white-space:nowrap; overflow:hidden;}
</style>
</head>
<body>
<!-- cover begin -->
<div id="coverpage">
<div id="onepics"><div class="onepic_wrap"><img src="images/header.png" class="wrap_pic"></div></div>
<!-- 文字介绍 start -->
<div class="onepic_bg">
<p id="onepic_sum">居民被迫撤离，主要州际高速路关闭。摄影：Darvi</p>
</div>
<!-- 文字介绍 end -->
</div>
<script type="text/javascript">
var win_height; //浏览器当前窗口可视区域高度
var win_width; //浏览器当前窗口可视区域宽度
var original_width = 2100; //图片原始尺寸，编辑可手填
var original_height = 1000; //图片原始尺寸，编辑可手填
var pic_width, pic_height, pic_left ,pic_top; //裁剪适配后的图片显示尺寸和左边距、上边距
OnePicAction();
function OnePicAction(){
win_height = $(window).height(); //浏览器当前窗口可视区域高度
win_width = $(window).width(); //浏览器当前窗口可视区域宽度
//裁剪图片
if(Math.ceil(win_height * original_width / original_height) < win_width ){
pic_width = win_width ;
pic_height = Math.ceil(win_width * original_height / original_width);
pic_left = 0;
pic_top = - Math.ceil((pic_height - win_height) / 2);
}else{
pic_height = win_height;
pic_width = Math.ceil(win_height * original_width / original_height);
pic_left = - Math.ceil((pic_width - win_width) / 2);
pic_top = 0;
}
$("#onepics .wrap_pic").css("width",pic_width+"px").css("height",pic_height+"px").css("margin-top",pic_top+"px").css("margin-left",pic_left+"px");
}
//浏览器大小变化时壹图处理
window.onresize = function(){
OnePicAction();
}
</script>
</body>
<html>
jquery我单独拿出来吧
<script type="text/javascript">
var win_height; //浏览器当前窗口可视区域高度
var win_width; //浏览器当前窗口可视区域宽度
var original_width = 2100; //图片原始尺寸，编辑可手填
var original_height = 1000; //图片原始尺寸，编辑可手填
var pic_width, pic_height, pic_left ,pic_top; //裁剪适配后的图片显示尺寸和左边距、上边距
OnePicAction();
function OnePicAction(){
win_height = $(window).height(); //浏览器当前窗口可视区域高度
win_width = $(window).width(); //浏览器当前窗口可视区域宽度
//裁剪图片
if(Math.ceil(win_height * original_width / original_height) < win_width ){
pic_width = win_width ;
pic_height = Math.ceil(win_width * original_height / original_width);
pic_left = 0;
pic_top = - Math.ceil((pic_height - win_height) / 2);
}else{
pic_height = win_height;
pic_width = Math.ceil(win_height * original_width / original_height);
pic_left = - Math.ceil((pic_width - win_width) / 2);
pic_top = 0;
}
$("#onepics .wrap_pic").css("width",pic_width+"px").css("height",pic_height+"px").css("margin-top",pic_top+"px").css("margin-left",pic_left+"px");
}
//浏览器大小变化时壹图处理
window.onresize = function(){
OnePicAction();
}
</script>
原文：http://www.cnblogs.com/bestsamcn/p/4941224.html