Gemini Man is a film that has been in the works for at least 12 years, having been stuck in development hell for until production on this current version began in 2017. The reason it took so long to get made was because the idea of having an actor face off against a younger clone was deemed to difficult to accomplish - the technology just wasn't right to realistically take an actor and make him look younger.
But with the way de-aging tech has progressed over the past decade or so, Gemini Man has actually been made featuring Will Smith as Henry Brogan, a newly-retired assassin facing off against a 23-year old clone of himself named Junior. De-aging may not be a new thing any more, but the way Gemini Man approached the challenge of Smith vs Smith is a little bit different to what other films have done.
To find out more about how things were done, I spoke to Gemini Man's VFX Supervisor Bill Westenhofer and get the low down on how they took one older Will Smith and had him appear on screen against his younger self.
Obviously, as is the way with digital characters, there was a stand-in who played Junior on set. That way the other actors, particularly Will Smith, weren't just acting and reacting to thin air. It also made life easier for the VFX team as well, since they already had some sort of performance to work from when composing the final shot. That being said, because of the way Gemini Man's de-aging tech worked, you won't actually see any of him in the film. That's because Junior himself is 100% CGI.
You might have thought de-aging worked by adding a younger face into a different body, or with extensive make-up work, but in this film that wasn't really feasible. Bill explained that the high resolution of the film (4K vs the normal 2K) and the increased 120fps frame rate meant that it was a lot easier to notice inconsistencies on screen. You can't just add a bit of make-up onto Smith and make him look 25 years younger like you could with an actor who hasn't changed a lot over the past couple of decades, like Samuel L Jackson in Captain Marvel, for instance. It was still visible on screen, and that wasn't going to work.
Head swapping was apparently discussed early on in production, but the results of that were deemed too awkward, as acting is shown off as much in the actor's body as it is in his face. And because the body and facial performances work together in tandem , simply sticking Will Smith's face onto a double's body is going to come across as awkward and somewhat unbelievable. Though with the advances in creating life-like animated characters, it's not actually hard to believe that it could be done with a real person. One example Bill mentioned to me was the new Planet of the Apes series, though there are plenty more examples of it happening with animals and aliens. Just look at Professor Hulk in Avengers Endgame, or even Gollum in Lord of the Rings, and you can see what they're talking about.
So Junior was built from scratch, with some help from Will Smith in a mo-cap suit, to generate the younger character. Naturally that came with plenty of challenges.
The main challenge was to create a digital character that was believable as a real person, and not one that's going to cause the audience to jump head-first in a two hour trip to the Uncanny Valley. Then, of course, you had the issues of making that character look exactly like Will Smith did back in his younger days. Thankfully, like a lot of de-aged actors, the VFX team did have a lot of footage to refer back to, including the likes of The Fresh Prince of Bel Air and Independence Day.
Of course the high frame rate didn't do make life any easier, since all those extra frames meant more work creating all the effects properly. Overall the task took an entire year to complete, and heaviest use of the CGI was Junior himself - for obvious reasons. But Bill says that the extra frames actually helped improve the quality of the film. The animation itself is a lot smoother when you have to add in all those extra frames, and that's visible regardless of whether you see the film in 120fps or the lower 60fps and 24fps frame rates. Which makes sense, because like with downscaling video content all that extra information doesn't go away, you're just viewing it differently.
But despite all their efforts, the VFX team still felt that something was slightly off with the way Junior was portrayed on screen. But when comparing the footage they'd created with some of the more dramatic scenes from his early acting days it turns out there wasn't anything specifically wrong with the visuals. As it turns out, Bill told me that because most people know the younger Will Smith as playing happier and more care-free characters, it felt strange to see the younger version of him playing a very dramatic and serious role like Junior.
Fight scenes were a totally different story, though, because erasing one fighter for replacement and not the other adds a whole new layer of complications into the mix. So, to make life easier, the VFX team just went ahead and animated the whole lot - with both Smiths old and new added into the film with computer wizardry. Though that's not to say those fight scenes weren't based in reality.
Director Ang Lee mandated that he wanted the fights to look real, and not like a pre-rehearsed 'dance' where the stuntmen involved knew exactly what choreographed moves were coming and when. So the fight scenes came about thanks to the stuntmen in question just going at each other on camera, first on set and then again with motion capture equipment. Once that was done they could erase them from the on-set footage and reanimate the fight scenes with the mo-cap footage and put it into the film itself. And when it comes down to creating two people fighting, once you nail the task of creating a computerised version of '90s-era Will Smith, adding a second Smith into the mix probably isn't a huge deal.
Of course the filmmakers did their best not to over-rely on CGI. Partially because you need to put in all the extra effort to make it look right in the hi-res high framerate format, but also because CGI still can't offer the same level of detail as practical effects do when they're on camera. Of course there are the instances where this isn't possible, like all the aforementioned effects and creating Junior. Though Bill says he believes the de-aging process shouldn't be something that's done just for the sake of it, and should actually play into the story of the film. Like here, where you couldn't possible have had Old Smith vs Young Smith without it.
But after all that effort to turn Smith into his younger clone, some people may be thinking that there are easier ways to do it, right? The news has seen a lot of talk about Deep Fakes, which uses AI to stick new faces onto existing bodies to create a whole new performance. Well according to Bill Deep Fakes can only get you 90-odd percent towards a truly believable image, and while it may seem easier and faster to do that the last few percent needs enough work that (right now, at least) it's easier just to build the whole thing from scratch.
So don't go expecting to see any Deep Fake-powered effects in big-budget movies for a while. As Bill explained to me, it's always easier to have a real person in front of the camera. Computer effects are great and everything, but you can't just replace Will Smith. After all, barring the effects that brought him to life, Junior's on-screen performance was all down to the man himself. Smith actually worked with Ang Lee to get himself back into the younger mindset, not only to play a younger version of himself but also to draw on his own childhood experiences to add more depth the Junior as a character.
So while visuals are great, we're nowhere near the stage where we can ditch the people behind them.
Gemini Man is in cinemas now.