Angular:ng-src动态图片js中获取不到宽高
<div class="content-1" ng-repeat="obj in rows">
<div class="img-3" style="position: relative;overflow: hidden">
<a ng-href="/opus/{{obj.feedId}}"><img class="im" ng-src="{{obj.opusImage}}" alt="" style="max-width: 100%;height: 100%;" class="im"/></a>
</div>
<div class="text-5">
<div style="font-size: 16px" ng-bind="obj.opusWord"></div>
<div style="margin-top: 20px;" ng-bind="obj.opusDesc"></div>
</div>
</div>
var left=-($(".im").width()-550)/2;
var top=-($(".im").height()-368)/2;
$(".im").css({left:left,top:top});
这里图片的宽高都是null,怎么才能获取到呢