adding image buttons in linear layout slowed down the app

i was trying to add image buttons in a vertical linear layout to get an interface similar to cnet mobile app. i ended up with java heap exception. now the app loads and the scrolling is very slow and sometimes the app force closes.`

<LinearLayout 
        android:id="@+id/container"
        android:orientation="vertical" 
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"

        >


<ImageButton
    android:id="@+id/imageButton1"
    android:layout_width="fill_parent"
    android:layout_height="200dp"
     android:src="@drawable/dt1"
    android:onClick="a"
    />

<ImageButton
    android:id="@+id/imageButton2"
    android:layout_width="fill_parent"
    android:layout_height="200dp"
    android:src="@drawable/dt2" 
    android:onClick="b"/>



<ImageButton
    android:id="@+id/imageButton3"
    android:layout_width="fill_parent"
    android:layout_height="200dp"
    android:src="@drawable/dt38" 
    android:onClick="c"/>

<ImageButton
    android:id="@+id/imageButton4"
    android:layout_width="fill_parent"
    android:layout_height="200dp"
    android:src="@drawable/dt4" 
    android:onClick="d"/>

<ImageButton
    android:id="@+id/imageButton5"
    android:layout_width="fill_parent"
    android:layout_height="200dp"
    android:src="@drawable/dt5" 
    android:onClick="e"/>

<ImageButton
    android:id="@+id/imageButton6"
    android:layout_width="fill_parent"
    android:layout_height="200dp"
    android:src="@drawable/dt6"
    android:onClick="f" />

<ImageButton
    android:id="@+id/imageButton7"
    android:layout_width="fill_parent"
    android:layout_height="200dp"
    android:src="@drawable/dt7" 
    android:onClick="g"/>

`