function initimg(parpic,maxwidth,maxheight)
{
var scale=maxwidth/maxheight;
var realscale=parpic.width/parpic.height;
if((parpic.width>maxwidth)||(parpic.height>maxheight))
{
if(realscale>scale)
{
parpic.width=maxwidth;
}
else
{
parpic.height=maxheight;
}
}
}

//根据id取得对象
function $(id){

return document.getElementById(id);
}