I know exactly what you mean and I think to be honest it's a bit like a shell. The people you love and trust you show them the real you but people you don't know so well see you differently.
The idea of masks could be more with the fact that we have different things that we want certain people to see. Like, my close friends & family can see my raw essence of who I am, whereas at work they only know me as the bright happy girl.
These masks can be used as defense, to protect us from hurt, betrayal etc too. I really like this and how you've just actually thought this over.
I mean, looking at what some people view me as I am rather shocked, because I know that is only one fraction of who I am as an individual.