//图片按比例缩放
var flag = false;
function DrawImage(ImgD, iwidth, iheight) {
    //参数(图片,允许的宽度,允许的高度)
    var image = new Image();
    image.src = ImgD.src;
    if (image.width > 0 && image.height > 0) {
        flag = true;
        if (image.width / image.height >= iwidth / iheight) {
            if (image.width > iwidth) {
                ImgD.width = iwidth;
                ImgD.height = (image.height * iwidth) / image.width;
            } else {
                ImgD.width = image.width;
                ImgD.height = image.height;
            }
        }
        else {
            if (image.height > iheight) {
                ImgD.height = iheight;
                ImgD.width = (image.width * iheight) / image.height;
            } else {
                ImgD.width = image.width;
                ImgD.height = image.height;
            }
        }
    }
}

//用法：<img src='' alt='' onload="resizeimage(this)" />
function resizeimage(objImg) {
    var w0 = 0;
    var w1 = 400;
    var h0 = 0;
    var h1 = 0;
    if (objImg.width > w1) {
        w0 = objImg.width;
        h0 = objImg.height;
        h1 = w1 / w0 * h0;
        objImg.style.width = w1;
        objImg.style.height = h1;
    }
}