js控制图片按比例缩放

<script type="text/javascript">
//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;
}
ImgD.alt = image.width + "×" + 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;
}
ImgD.alt = image.width + "×" + image.height;
}
}
}
</script>
页面代码：
<img onload="javascript:DrawImage(this,89,63)" src="http://www.jb51.net/images/logo.gif" width="89" height="63" border="0" />