android background image slows down app

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http://stackoverflow.com – I am using a viewpager to swipe amongst fragments in my app. I define the background in the XML, so android:background="@drawable/bg_final" If I use a simple background color, my app works very smooth. If I use it with this background image, fps decreases and my app becomes only passable. It is not slow, just not so smooth, however on weaker devices it could work laggy. Is it a bad way to apply a background image? The whole image is a 480x800 png with the size of 14.7kB. What might be the problem? (the backgrounds of the fragments are transparent, the viewpager is in a main.xml which has (HowTos)