For example, you don't think about how cinematographer Matty Libatique's cameras got so close to all the actors while they were dancing in those mirrored rehearsal rooms. (This required elaborate "clean up.") Or how those images in the mirror got turned around. Or how those crazy pictures in Nina's mother's room came alive--without making us laugh. Faces, mouths and eyes are animated, as are the tattoos on Mila Kunis's rippling back.
The feathers poking out of Nina's back were prosthetic, but the mesh of bumps was digital. Nina sticks a retractable prop into Beth's spongey prosthetic face, which spurts fake blood: the VFX folks turned it into an emory board. And that nasty hang nail is a "digitally enhanced" hand prosthetic with "added blood." While Portman deserves kudos for her extreme training and on-point ballet dancing, some of her more complex steps were handled by another dancer repeating the same moves, whose head had to be seamlessly replaced by Portman's (see photo gallery below). "We'll never know how much," admits Visual Effects Supervisor Dan Schrecker.
When Portman is fitting her costume in the dressing room, two back-to-back mirrors create infinite reflections. One of them--the third--is out of sync. They used two one-way mirrors so the camera is not seen, but you still see the mirrored reflections. It was a simple camera move right to left, one master take. The VFX people took out one mirror and did the same shot against a green screen. They isolated the element, removed the real reflection, and put in the green-screen element. Some of the mirror reflections were also thrown out of sync when she was dancing alone in the rehearsal hall. At one point she moves her arm and the reflection does not. At the end you see the evil Nina double in the mirror.
The sequence when Nina's bird legs snap backwards was done with puppet legs against a green screen combined with Portman's body.
The Black Swan finale took a long time to finalize with Aronofsky. "To what extent would she become a swan?" says Schrecker. "Neck, wings, head, neck? Human or swan head? At one point she had a facial bill. We tried all the permutations. It's a beautiful moment for Nina. So we keep that image, just wings and Natalie herself. We kept the veracity of the ballet and used motion capture tracking the dancer. We had the data. The artist took control and built wings and feathers arranged in layers as the swan anatomy stretched and grew."
Here's a trailer.