Android : keep aspect ratio of background image (android)

i have a background image which should be scaled on the height, but keep its aspect ratio. i tried it whith this code:

<ImageView
        android:id="@+id/iv_background"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="centerCrop"
        android:src="@drawable/bg" />

this works on phones in potrait mode, but when i test it on a tablet (default landscape), it scales the width and cuts the image on top and bottom. is this because of the xml code or because of the landscape?