Backgroundimage in the header and footer of a TabbedPage

I am merging an IOS/Android project written before xamarin.forms where available to use only xamarin.forms.

I can't figure out how to put a background image in the header (where the title is) and the footer (behind all the icons and text) when using a TabbedPage.
Each Tab contains a NavigationPage. Im not using XAML.

Can anybody point to a piece of code to look at?

Best regards