Android : Android: XML size does not match dimension size

In my layout folder, I have the following main XML:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

<ImageView
    android:id="@+id/img"
    android:layout_height="@dimen/dimension"
    android:layout_width="match_parent"
    android:src="@drawable/ic_launcher"/>

</LinearLayout>

The problem is the height is not what I would expect it do be when I run the program. My values/dimens.xml specifies what the actual height is:

<resources>
    <dimen name="dimension">32dp</dimen>
</resources>

And in my code, when I view the height ImageView height in pixels and the dimension size in pixels, they differ:

View v = findViewById(R.id.img);
Log.e("Image height in px", "" + v.getHeight());//64

Resources r = getResources();
Log.e("Dimension in DP)", "" + r.getDimension(R.dimen.dimension));//64
int dimension = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, r.getDimension(R.dimen.dimension), r.getDisplayMetrics());
Log.e("Dimension in PX", "" + dimension); //128

Why isn't the ImageView the same height as the calculated height?