In Legend starring Tom Hardy, he plays both Kray twins, so how exactly did they film the section in the bar where they fight each other? I know some of the framing only has one of their faces in it but from what I remember that there are parts where both faces are in it. I'm assuming CGI but could anyone help?
They used fixed and computer controlled motion cameras to get the exact same filming sequence, and filmed it twice with the actor in different positions.
One article is here, there are several similar articles around on the net. The fixed camera technique has been used quite a few times. The article denotes one such was done in the original Parent Trap, where they filmed it with an actress and a body double, then refilmed and combined them later in the editing room.