With today's digital effects technology, it seems that there is essential nothing that can't be done in the movies. In the upcoming film Gemini Man, we'll actually see Will Smith fighting a younger version of himself, but the specific digital effects being used to make that happen may not be the ones that you think. The young version of Smith is created entirely with CGI, rather than "de-aging" the actor. According to Smith...
The younger character is not me. That is a 100 percent digital character. A completely recreated character. They didn’t take my image and just stretch some of the lines. It is a completely CGI character in the same way that the lions in The Lion King are CGI characters.
When we all saw the first trailer for Ang Lee''s Gemini Man we all likely thought the same thing. Will Smith is actually the one behind both roles, and when he's playing his younger self, his face is being digitally de-aged, the same way that Marvel Studios has made Michael Douglas look younger when necessary.
However, at a recent Gemini Man Q&A (via Slashfilm) Smith made it clear that's not the case. While Smith did do motion capture for the younger character, it seems that all that was only data, which, when combined with the reference material of Will Smith's early films and TV work, led to the creation of the younger version entirely inside the computer. As Smith says, just as the animals in the new Lion King were created.
Based on what we've seen in the trailers for Gemini Man it's pretty impressive work for being an entirely CGI human. We've seen the technology before in recent films like Rogue One: A Star Wars Story. In those cases entirely different actors were used to build CGI versions of Peter Cushing and Carrie Fisher.
Neither of them was perfect, but they were solid, and both only had small parts in the movie, so any "uncanny valley" issues didn't detract too much from the finished film. That won't be the case here. In Gemini Man the young Will Smith is a major character who is going to be all over the movie. Not only that, we're going to have modern Will Smith standing next to him so we'll be able to clearly see what the real thing looks like. If the CGI doesn't work, it's going to be a major problem for the movie.
It seems like the de-aging route might have been easier, so it's not entirely clear why Ang Lee decided to go full CGI, beyond the fact that the director is fan of using new technologies and pushing the envelope of what is possible in film.
Now that we can create photo realistic animals like The Lion King and nearly photo realistic humans, it seems there really is nothing we can't do with CGI. Animation has always been the way to make anything happen in the movies, and with CGI we're basically doing a type of animation that just happens to look like the real thing.
Gemini Man hits theaters October 11.