The first trailer for "Alita: Battle Angel" debuted in December 2017.

After its release, visual effects supervisor Eric Saindon recalled receiving fan criticism about the eyes looking too big or not looking accurate on the humanoid main character.

The VFX team told Insider they spoke with producer James Cameron and director Robert Rodriguez about whether or not they should shrink the eyes.

They didn't. As a result of criticism, they wound up enlarging Alita's iris and limiting the amount of white in the eyes.

"All the changes that happened afterward were not about, you know, pandering to the noise in any way. It was about bettering the character," visual effects supervisor for Lightstorm Entertainment Richard Baneham told Insider.

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Making Alita, the humanoid main character in "Alita: Battle Angel," work next to live-action characters onscreen was the biggest challenge for the visual effects team to bring to life in the film.

You may not have realized it, but a lot of work went into making the character's big, bright brown eyes look just right, especially after the film's first trailer.

"We had our original design, all based on the original artwork and [producer] Jim [Cameron]'s artwork and [director] Robert [Rodriguez]'s artwork, and even after the first trailer that came out, we got some criticism online about, 'Hey, the eyes are too big. They don't look right. Uncanny valley,'" visual effects supervisor Eric Saindon told Insider during a visual effects press day for the film at the Walt Disney Studios lot.

Here's how Alita looks in the first trailer released for the film. 20th Century Fox

Based on the Japanese manga series "Gunnm," the film follows a female cyborg, Alita, who has trouble remembering her past.

Saindon said the visual effects team spoke with Cameron and Rodriguez after the trailer came out in December 2017 to see what they thought of the criticism and whether or not they should change Alita's look at all as a result.

"'Do we want to shrink the eyes?'" Saindon said. "They came back and both said, 'Absolutely not, we're going to go bigger on the eyes.'"

"We didn't actually go bigger on the eyes, but we did enlarge the iris," Saindon continued. "We reduced the amount of sclera, the white around the eyes, and it sort of just popped everything back together. It popped her to be that manga character, but to be able to sit next to a live-action character. You never questioned it."

You can see how Alita changed from that first trailer to the final film here. It's a subtle change you may not have noticed:

Alita's face is also softened a bit more in the final film. The lighting in this scene is a bit brighter on her face now. 20th Century Fox

Why Alita's eyes were the most important to get just right

For the team, it was important to get the eyes right because not only is that the first thing you see when you meet Alita, but they believed that was going to be one of the main things that helped sell the believability of the character to audiences.

"Eyes are really critical in an actor's performance," said animation supervisor, Mike Cozens. "That's why, you know, as shots get more intimate, we cut in closer and closer... Eyes are sort of what are telling you what's going on inside the head, keeping that performance alive in the eyes, beyond the design and into performance was really critical, a critical part of the storytelling."

Here's how Alita looks when she opens her eyes for the first time in the films first trailer versus the final film. 20th Century Fox

"Truly, the eye size shouldn't matter," added visual effects supervisor for Lightstorm Entertainment, Richard Baneham. "Ultimately, when we look at a screen, I think it's point-four of a second for us to read whether there are eyes onscreen or not. We immediately, as humans, go to that, because we want to understand how somebody is emotionally, what their state is. It's what we do when we meet people, it's how we read the room."

Baneham said that regardless of the eye size, you can usually tell a person's emotional state almost instantly through posture and their facial expression. That's why it was important to get Alita's eyes just right.

"So long as you communicate properly the emotional state of the character, the eye size, not that it's irrelevant, it shouldn't be the thing that's in the way," added Baneham. "We often say on our side, you don't smile with your face, you don't smile with your mouth, you smile with your eyes... As soon as you, you can cut to a pair of eyes and tell whether somebody's smiling."

If you covered up everything but Alita's eyes in this image, you would be able to tell she's smiling. 20th Century Fox

This isn't the first time a trailer's criticism has resulted in changes to a film.

After the release of the first trailer for the Sonic the Hedgehog film in April 2019, the video game character's design sparked criticism and jokes online.

As a result, the film's director, Jeff Fowler, said Paramount and Sega were going to redesign the character and the movie was moved back four months to February 2020 "to make Sonic just right." In November, a new and more recognizable design for the character was revealed, satisfying fans.

The image on the left shows Sonic's original design. The image on the right shows how Sonic looks after the redesign. Paramount Pictures

How does the "Alita" visual effects team feel about receiving audience criticism right away after a trailer's release?

"I didn't mind hearing input from the outside world. It really solidified us, though," said Saindon of reactions to the first trailer. "It kind of got everybody together and the real choices that were made beforehand kind of held. There was hardly any change, if you will, because I remember having, we had various different sizes and stuff out there and we were pretty big on the trailer, and it just kind of stayed there. It just made everybody reconsider what they were doing."

"Whether she had big eyes or not, towards the end, I think all of us realized it was worthwhile worrying about it, and certainly it's all about this expression that's getting through or not getting through and worrying about that."

Most of Alita's design comes directly from the performance of actress Rosa Salazar who embodies the character. 20th Century Fox

Baneham added that it's about making sure the audience invests in the character and comes along for the journey.

"That's what you care about first and foremost, is making sure when the audience watch the movie, they're not thinking about the technical aspects of the movie in any way, sort or form. They go on this, hopefully, immersive journey with the character," said Baneham of what he wants viewers to get out of watching "Alita."

"All the changes that happened afterward were not about, you know, pandering to the noise in any way. It was about bettering the character," Baneham added.

"Alita: Battle Angel" is one of 10 finalists in the visual effects category at the 92nd Academy Awards. The Oscar nominations will be announced Monday morning.