No, you don't have to seperate the even/odd bytes, that would affect the speed. You don't need to know the png file structure either.
You just still use the same InputStream methods to read everything back, the only thing you need to know is where to start read, where to finish. Those are your companies convention,
you should not let anyone else to know. For the same reason, I cannot give you sample code.
Be creative, that is it!!!