De-aged versions of Linda Hamilton, Arnold Schwarzenegger and Edward Furlong appear in the film thanks to the handiwork of VFX experts (one worked on Brad Pitt a decade ago in 'The Curious Case of Benjamin Button').

This year's visual effects shortlist is rife with nostalgia as several films feature de-aged actors: The Irishman's Robert De Niro, Al Pacino and Joe Pesci; Gemini Man's Will Smith; Captain Marvel's Samuel L. Jackson; Avengers: Endgame's Robert Downey Jr. and others; and Terminator: Dark Fate's Linda Hamilton, Edward Furlong and Arnold Schwarzenegger.

In the VFX shortlisted Terminator: Dark Fate, directed by Tim Miller — the latest installment in the Paramount series — viewers reconnect with Sarah Connor (Hamilton), John Connor (Furlong) and the T-800 (Schwarzenegger) in a flashback set a few years after the events in 1991's Terminator 2: Judgment Day, setting up the story in Dark Fate.

Eric Barba, the film's VFX supervisor, wasn't new to the formidable challenges of de-aging work; he won an Oscar for aging Brad Pitt in reverse in 2008's groundbreaking The Curious Case of Benjamin Button. But a decade later, it remains a complex task that continues to advance through technical innovation and artistic experience. "I look back at Benjamin Button and the tools that we had, and I don't know how we got it that good," Barba admits. "Ten years later, we are still pushing that envelope. It's still really hard."

There are various approaches used to de-age actors in movies. For the flashback sequence in Dark Fate, the team did digital head replacement on younger actors who functioned as body doubles and were filmed on set. The digital work started with a scan of each original actor. Then the team used a markerless facial capture system called Anyma, developed by Disney Research, to capture each actor's performance.

Using lead VFX house Industrial Light & Magic's Blink software, the artists then applied these nuanced performances to de-aged heads of the original actors. "We change in subtle ways as we age," Barba explains. "We constantly tested it against the older films."

Visual effects supervisor Jeff White of ILM adds that they used artificial intelligence tools to analyze the work in progress. They also got some help from Schwarzenegger himself. "When we were doing some additional photography, I showed some of the [digital head] shots to Arnold," says White. "He said, 'Looks great from the nose up, but the mouth shape was wrong. I'd never do something that puckered.' " With his guidance, they made subtle adjustments.

Barba says they captured each actor's facial performance using Sony's Venice camera, shooting 4K at a high frame rate of 48 frames per second, which he considers the minimum resolution and frame rate that should be used for this purpose. "It's crucial when you are trying to re-target and animate to another face, you need those subframes to get all of the intricacies for the human face, so it doesn't feel a little 'Botox-y' or that something's not quite right. It makes a big difference in what you ultimately get."

In all, the Dark Fate VFX team completed 1,900 shots but kept their focus on the franchise stories' past when advancing both the story and the technology. Says Barba, "We wanted to honor and build upon" what ILM did for T2.

This stor appears in a January stand-alone issue of The Hollywood Reporter magazine. To receive the magazine, click here to subscribe.