jquery控制图片按比例缩放

$(function() {
        var boxWidth = 675;
        var boxHeight = 450;
        var imgWidth = $("#img1").width();
        var imgHeight = $("#img1").height();
        //比较imgBox长宽比img长宽比
        if ((boxWidth / boxHeight) >= (imgWidth / imgHeight)) {
            //重新设置imgwidthheight
            $("#img1").width((boxHeight * imgWidth) / imgHeight);
            $("#img1").height(boxHeight);
            //让图片居显示
            var margin = (boxWidth - $("#img1").width()) / 2;
            $("#img1").css("margin-left", margin);
        }
        else {
            //重新设置imgwidthheight
            $("#img1").width(boxWidth);
            $("#img1").height((boxWidth * imgHeight) / imgWidth);
            //让图片居显示
            var margin = (boxHeight - $("#img1").height()) / 2;
            $("#img1").css("margin-top", margin);
        }
    });