xamarin forms image by theme code example
Example: How to have scalable images using image view xamarin XML
//XML Xamarin ImageView scalable image
<ImageView android:id="@+id/topLogoImg"
android:src="@drawable/topLogo"
android:focusable="false" android:padding="0dp"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:scaleType="fitCenter" />