Center the ion-scroll on page

I am using ion-scroll directive to create pinch-zoom feature on image. It works well. My images however can be portrait or landscape and thus want to center the image in the scroll-view and use pinch and zoom.
Here is the screen shot of how it appears now

Here is the code I am using

<ion-scroll zooming="true" min-zoom="1" direction="xy" >
    <img  ng-if="photo.type === 'image'" data-src="photo.path" data-url="{{mURL}}" class="full-image mPlaceholder center" alt="" load-cached-photo  on-swipe-left="onSwipeLeft()" on-swipe-right="onSwipeRight()"></img></ion-scroll>