等比缩放图片并居中

var flag = false;
function DrawImage2(ImgD) {

//alert(ImgD.style.height);

    var image = new Image();
    image.src = ImgD.src;
    if (image.width > 0 && image.height > 0) {
        flag = true;

        if (image.height > 150) {
            ImgD.height = 150;
            ImgD.width = (image.width * 150) / image.height;
        } else {
            ImgD.width = image.width;
            ImgD.height = image.height;
        }
		
		
		if(ImgD.height==150){
			ImgD.style.marginLeft=(200-ImgD.width)/2+'px';
		}else{
			ImgD.style.marginTop=(150-ImgD.height)/2+'px';
		}


    }
}