Moviegoers saw another example of the technology being used last month, when James Gunn's Guardians Of The Galaxy Vol. 2 introduced a young Kurt Russell as his character, Ego. Walt Disney Pictures and Marvel are clearly comfortable with taking this route, as they have also brought audiences a young version of Michael Douglas in Ant-Man (2015) and Robert Downey Jr. in Captain America: Civil War (2016).
"It definitely seems to be a trend," says Industrial Light & Magic animation supervisor Hal Hickel, who won an Academy Award® for Pirates Of The Caribbean: Dead Man's Chest (2006) and recently completed Rogue One: A Star Wars Story (2016). "It may be because it's been done successfully and filmmakers realize it's an option in telling a story, or maybe it has opened up an option that they need."
For Ed Ulbrich, president of visual effects and virtual reality at Deluxe (the parent of visual effects houses Method an Iloura), the use of this sort of work can be attributed to this "age of franchises, and the franchises are prequels and sequels and spinoffs. These stories go omnidirectional in time. Some of the characters become iconic. But we all get older."
"It's very unforgiving – you either get it right or it's glaringly obvious," says Weta visual effects supervisor and two-time Oscar nominee Guy Williams (Guardians Of The Galaxy Vol. 2) of these techniques.
So how exactly does it work?
Methods vary, but Christopher Townsend, visual effects supervisor on Guardians Of The Galaxy Vol. 2, explains the creation of the digital Kurt Russell, created by one of the film's digital effects houses, Lola, which has earned a reputation for specialising in this sort of work. It started with collecting and examining 1980s photos of Russell as well as his films from that period, such as Big Trouble In Little China (1986), to come up with the desired look.
Next, director James Gunn and Lola cast actor Aaron Schwartz – in making the decision, Lola identified several actors with similar facial structure and Gunn brought them in for screen tests.
For filming, both Russell and Schwartz were identically dressed and makeup was applied to Russell to give him a younger appearance, with both actors wearing tracking markers on their faces for reference. First Russell performed the scene, and then Schwartz would step in and perform the same scene, mimicking what Russell did. Through visual effects, these takes were combined with some additional digital effects to create the final look and performance, frame by frame. "We cut and pasted pieces of Aaron's geometry," Townsend explains. "The geometry of the face changed, for instance his neck became fuller. We reshaped the jaw, chin, neck, lips – very specific details. It involved understanding the physiology of the human face.
"The technology is getting better, but it's really the artists, that's the key," he emphasised. "It was a huge amount of work – months and months of artists working at computers."
The digital Robert Downey Jr. from Captain America: Civil War and digital Michael Douglas in Ant-Man were both used for flashbacks and achieved in much the same way, says Townsend, who was also visual effects supervisor on those films.