I don't understand the problem... but i'll try to make and answer for that.
when you use imageView you can set this attributes
scaleType="fitXY"
adjustBounds="true"
That will center your image view and resize to XY if is necessary. But please remember that you need to use src="" and not setbackground in the image view.
Well with this clear we'll proceed with RelativeLayout
Make a parent for example a FrameLayout, inside make a relative layout this (nesting is not necessary but for now we'll use it).
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
>
<ImageButton
android:layout_alignParentTop="true"
android:layout_alignParentRight="true"
android:src="@drawable/ic_add"/>
<ImageView
android:layout_width="match_parent"
android:layout_width="wrap_content"
android:adjustViewBounds="true"
android:scaleType="fitXY"
android:src="@drawable/ic_add"
/>
</RelativeLayout>
i don't test it but thats the main idea.