The look, movement and subtle signals from a human face are things we all know on a deep, even subconscious level. The face of someone we know personally or the face of a famous person is even more ingrained in our memories. And this is exactly what made the visual effects on “I, Tonya” such a huge challenge.

Eight VFX, which worked on the film with helmer Craig Gillespie, needed to find a way to get the best possible scans of Margot Robbie so that her face could be rebuilt in 3D and matched to the body of a skating double who would do the most complicated and dangerous skating moves in the Tonya Harding drama.

“When you’ve got a real person in the movie and you’ve got to do a face replacement that looks perfect, that’s quite a challenge,” says Juliet Tierney, head of production at Eight VFX and VFX producer on “I, Tonya.” “There was one really long shot toward the end of the movie that’s made up of three different shots.

There’s the first one that’s Margot skating for real and the middle one is the body double where the tricks get more complicated and the last take is Margot again. So, having Margot and then face replacing Margot into one seamless shot is a lot of pressure to make it look perfect.”

Tierney brought in French company Eisko, which had scanning rigs that were especially powerful and accurate, during the shooting. This laid the groundwork for the post process down the pipeline. Eight VFX used 2D and 3D techniques to craft the face replacements and its post crew used Maya, Flame and Nuke on the film.

“There were a number of shots close to camera so if they were shooting something with the body double we would green screen shoot the side of the ice rink and get Margot to replicate the facial expressions that she might make if she were skating that piece,” says Tierney. “We used tracking devices on the skating double — black marks on her face and an orange ball on the top of her head — to aid with tracking the face of the body double while she was skating so we could match them later.”

The company also set up six witness cameras around ice rink so they could pinpoint the movements of the skating double, rebuilt all the stadiums in CG and repopulated stadiums with CG people so they could match exact backgrounds from shot to shot.

With a tight turnaround of about six months to complete work on the film, Tierney and her crew were happy to come to set with a special advantage.

“We’ve been working with Craig [Gillespie] a long time on commercials before this, and it helped to have a shorthand with him because we had a sense of what he’d want, and we all wanted these face replacements to be perfect,” says Tierney.