图片居中

var divx = document.body.clientWidth;//获取当前页面的宽度
var divy = document.body.clientHeight;//
document.getElementById("big").src=obj_big;
var image=document.getElementById("big");
var divmove = document.getElementById("divbigimage");
divmove.style.left = (divx-image.width)/2+'px';//image.width图片宽度
divmove.style.top = (divy-image.height)/2+'px';

ps：

function getInfo()
       {
            var s = "";
            s += " 网页可见区域宽："+ document.body.clientWidth+" ";
            s += " 网页可见区域高："+ document.body.clientHeight+" ";
            s += " 网页可见区域宽："+ document.body.offsetWidth + " (包括边线和滚动条的宽)"+" ";
            s += " 网页可见区域高："+ document.body.offsetHeight + " (包括边线的宽)"+" ";
            s += " 网页正文全文宽："+ document.body.scrollWidth+" ";
            s += " 网页正文全文高："+ document.body.scrollHeight+" ";
            s += " 网页被卷去的高(ff)："+ document.body.scrollTop+" ";
            s += " 网页被卷去的高(ie)："+ document.documentElement.scrollTop+" ";
            s += " 网页被卷去的左："+ document.body.scrollLeft+" ";
            s += " 网页正文部分上："+ window.screenTop+" ";
            s += " 网页正文部分左："+ window.screenLeft+" ";
            s += " 屏幕分辨率的高："+ window.screen.height+" ";
            s += " 屏幕分辨率的宽："+ window.screen.width+" ";
            s += " 屏幕可用工作区高度："+ window.screen.availHeight+" ";
            s += " 屏幕可用工作区宽度："+ window.screen.availWidth+" ";
            s += " 你的屏幕设置是 "+ window.screen.colorDepth +" 位彩色"+" ";
            s += " 你的屏幕设置 "+ window.screen.deviceXDPI +" 像素/英寸"+" ";
            s += " window的页面可视部分实际高度(ff) "+window.innerHeight+" ";
            alert (s);
       };