In an interview with The New York Times, Lucasfilm explains the reason behind the decision to bring back faces from the past into Rogue One: A Star Wars Story, along with the technology that made the feat possible.

A word of warning that there are spoilers ahead, so for those who have not yet watched Rogue One, you might not want to continue reading.

Familiar Faces On Rogue One

For Rogue One, bringing back faces from the past does not simply mean the return of actors and actresses to take up the roles that they played in previous Star Wars movies. In the case of Grand Moff Tarkin, it meant the revival of the late Peter Cushing through cutting-edge technology.

Cushing, who played the role of the commander of the Death Star in 1977's Star Wars: A New Hope, passed away in 1994. However, the team behind Rogue One decided that it was important for Tarkin to be a part of the latest Star Wars movie.

"If he's not in the movie, we're going to have to explain why he's not in the movie," said Rogue One co-producer and Lucasfilm story development executive Kiri Hart in the interview.

How They Brought Back Grand Moff Tarkin

Initially, the filmmakers were not sure how they would have Tarkin in Rogue One. Solutions such as having Tarkin only appear in holograms or transferring his dialogue to other characters in the film were proposed, according to Rogue One producer and Industrial Light and Magic CCO John Knoll.

The method that the filmmakers ended up utilizing was having another actor, Guy Henry, perform onset as Tarkin. Henry acted out the role with full performance capture rigs mounted on his head.

Knoll explained that, using the information gathered from the rigs, they transformed the appearance of Henry into that of Cushing. However, Industrial Light and Magic quickly found out how challenging the work was, due to the difference in lighting between A New Hope and Rogue One and all the tiny details that they had to take into account.

This was the same technology that they used to film the late Carrie Fisher's Princess Leia in Rogue One as she appeared in A New Hope, with actress Ingvild Deila standing in for Fisher.

Is Cushing's Digital Revival For Rogue One Ethical?

Lucasfilm said that it acquired approval from the estate of Cushing before they revived the actor using CGI. However, die-hard fans and critics alike questioned the ethics behind the decision.

Knoll, in response, said that he knows about the "slippery slope" argument that, with how they revived Cushing for the role of Tarkin, other filmmakers might start to aggressively utilize the technique for more movies.

Knoll, however, said that due to the cost and effort behind the method, the revival of actors and actresses who have passed away is not something that can be done casually. He added that Industrial Light and Magic does not plan on utilizing such a technique extensively, as it only made sense for the company to do so for Rogue One.