Android Splash screen question

I need to display a splash screen on my Android app, but I need to have its proportions unchanged.

The tutorial shown on the Xamarin web site (http://docs.xamarin.com/guides/android/user_interface/creating_a_splash_screen) is using a style with a background image:

<resources>
  <style name="Theme.Splash" parent="android:Theme">
    <item name="android:windowBackground">@drawable/splash</item>
    <item name="android:windowNoTitle">true</item>
  </style>
</resources>

Unfortunatly, the image proportions are modified so it looks distorted on some screen resolutions. It looks like the image is displayed with the FitXY parameter. I would like the image to be scaled (liek fill_parent), but with its proportions unchanged (!fitXY)

How to achieve this?

Note : I tried to use different styles according to the device density (lp, hp, etc.) but it is not enough since this way I cannot handle all screen ratios.