ImageView in android XML layout with layout_height="wrap_content" has padding top & bottom

I have a vertical LinearLayout containing an ImageView and a few other layouts and views.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:contentDescription="@string/banner_alt"
        android:src="@drawable/banner_portrait" />

    <TextView
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:text="@string/main_search"
      android:gravity="center"
      android:textStyle="bold" />

    <LinearLayout
      android:orientation="horizontal"
      android:layout_width="match_parent"
      android:layout_height="wrap_content" >

      <Spinner
        android:id="@+id/search_city_spinner"
        android:layout_width="0px"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:prompt="@string/search_city_prompt"
        android:entries="@array/search_city_array" />

      <Spinner
        android:id="@+id/search_area_spinner"
        android:layout_width="0px"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:prompt="@string/search_area_prompt"
        android:entries="@array/search_area_array" />

    </LinearLayout>

    <LinearLayout
      android:orientation="horizontal"
      android:layout_width="match_parent"
      android:layout_height="wrap_content" >

      <Spinner
        android:id="@+id/search_rooms_spinner"
        android:layout_width="0px"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:prompt="@string/search_rooms_prompt"
        android:entries="@array/search_rooms_array" />

      <Spinner