JS按比例缩放图片

<script type="text/javascript" language="javascript">
var flag = false;
function DrawImage3(iwidth,iheight,ImgD) {
var image = new Image();
image.src = ImgD.src;
if (image.width > && image.height > ) {
flag = true;
//原图宽除高的值和定义宽除高的值的比较
if (image.width / image.height >= iwidth / iheight) {
// 原图的宽大于定义的宽
if (image.width > iwidth) {
ImgD.width = iwidth;
//定义的宽度和原图的宽度的比例，同比缩小高度
ImgD.height = (image.height * iwidth) / image.width;
} else {
ImgD.width = image.width;
ImgD.height = image.height;
}
ImgD.alt = image.width + "×" + image.height;
}
else {
// 原图的高大于定义的高
if (image.height > iheight) {
ImgD.height = iheight;
//定义的高度和原图的高度的比例，同比缩小宽度
ImgD.width = (image.width * iheight) / image.height;
} else {
ImgD.width = image.width;
ImgD.height = image.height;
}
ImgD.alt = image.width + "×" + image.height;
}
}
}
</script>

<img alt='' src="Image/wuqilong.jpg" onload="DrawImage3(200,150,this)" />