try this,
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ImageView
android:id="@+id/imageview"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="90"
android:background="@android:color/darker_gray"
android:scaleType="fitXY" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="10"
android:orientation="horizontal" >
<Button
android:id="@+id/button1"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="Ok" />
<Button
android:id="@+id/button2"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="Cancel" />
</LinearLayout>
</LinearLayout>