Which image extension is supported by a framework ? topic

Allright, i know my question could be strange but in fact i wanna know which image format could support framework-res.apk as PNG is the best format for a picture, i would like to know if i can convert all "Non-PNG" pictures into PNGs and if they will stay recognised by the apk. Sure it's not a huge space improvement but if i do this for all pictures, i'll probably have few MB away.

So thanks everybody :)