/*按比例生成缩略图*/
function DrawImage(ImgD, W, H) {
    var flag = false;
    var image = new Image();
    image.src = ImgD.src;
    if (image.width > 0 && image.height > 0) {
        flag = true;
        if (image.width / image.height >= W / H) {
            if (image.width > W) {
                ImgD.width = W;
                ImgD.height = (image.height * H) / image.width;
            }
            else {
                ImgD.width = image.width;
                ImgD.height = image.height;
            }
            ImgD.alt = "";
        }
        else {
            if (image.height > H) {
                ImgD.height = H;
                ImgD.width = (image.width * W) / image.height;
            }
            else {
                ImgD.width = image.width;
                ImgD.height = image.height;
            }
            ImgD.alt = "";
        }
    }
}