How, Exactly, Did Alita Make Rosa Salazar An Oddly Lifelike CGI Cyborg?

Upon first glance, Alita looks like any regular teenager just trying to play Motorball in the streets of Iron City. But take a closer look, and it’s hard to deny that Alita's eyes are maybe a little bit big for the average human face. That’s the first indication that Alita’s not your normal everyday teenager, and taking a closer look, yeah, Alita’s not even real at all. While she’s played by a real actress in Alita, motion capture has been fused with CGI to create a hyper-real performance, that seamlessly blends into the world. It looks incredibly real, and that’s the point. Alita: Battle Angel uses a lot of CGI, and not just for its titular star. Many characters in the movie are a mix of real and not real, whether it’s because they’ve got a robotic arm, a robotic body, or they’re entirely a robot themselves. Alita falls into this latter category, because even though Alita is played by Rosa Salazar, the actress never fully appears in the film. The cyborg hero is a creation all her own.

We’ve seen motion capture performances done in the past before — and the way Hollywood is going nowadays, we’re going to continue to see them. Characters from the Marvel Cinematic Universe have blended this real and CGI performance together, like The Hulk and Thanos. Mark Ruffalo and Josh Brolin play them, respectively, but they’ve been majorly overlaid with digital magic (Brolin even famously wore a floating Thanos head while he filmed to help with this).

Weta Digital, Peter Jackson’s studio that famously brought Gollum to life in the Lord of the Rings movies, is responsible for Alita’s look and performance, and instead of doing motion capture, they did something they call “performance capture.” As Producer Jon Landau explained in a behind-the-scenes video about Alita's CGI, “Simultaneously we’re capturing the body’s performance, [and] we’re capturing the facial performance.”

To do it, Salazar wore a motion capture suit, which is basically a black spandex suit with tiny little white dots all over it. The filmmakers placed cameras all around the set, to capture Salazar’s movement from every single angle they were filming. Later, the dots are used as reference points to animate the character and create what we see on screen. And on top of a body suit, Salazar also wore two high-definition cameras in a headset, pointed at her face, that would photograph her face to capture movements.

The reason to do this, instead of just creating something entirely out of CGI, is so that there is a human basis for the character. Director Robert Rodriguez and Landau promised Salazar she would see herself in Alita, even though it would end up being entirely digital. And she did: the first time Salazar saw the finished product in the trailer, she cried.

"I'm crying and also on the edge of my seat,” the Alita star told CNET. “I was so impressed because I got to see myself in this other body, but it is my body. But it's also like a whole new part of me to its own person."

Alita’s eyes proved to be one of the most challenging, and also rewarding, things to create for the characters. Yes, they’re bigger than most humans' are, but they still needed to be Salazar’s eyes. Everything about them had to be created from scratch, so Salazar’s eyes were actually scanned into the computer, to serve as a reference point for the animation.

As Eric Saindon, an FX supervisor at Weta Digital explained to Vulture, “What’s best is always to have an actor perform the eyes. To get the subtleties of the detail from an actor, it will always be the key. If you really watch the movement of someone’s eyes, they’re always weeping, they’re always fluttering, they’re always darting back and forth a little bit. They always have that little bit of extra motion that you don’t even notice.” Alita’s eyes went through 50 different variations before settling on a final look, the one we see on screen.

In the end, the process was weird to get used to for Salazar and drew some early criticism, but at least the actor herself loved it.