Sir Peter Jackson reveals what he learned from making WWI restoration film

He's made movies about hobbits, zombies and giant gorillas, but the subject of Sir Peter Jackson's newest film is much more real - very real.

The Kiwi director's new film about World War I hits New Zealand screens this weekend, bringing 100-year-old vision to life.

"You're seeing real people - their faces come alive," he told Newshub.

When Sir Peter was given free reign of London's Imperial War Museum archives to make a film four years ago, he became well aware of his deadline.

"Well you wouldn't want to miss the Armistice would you? 'Oh sorry, it's not gonna be ready 'til February next year!' It was not an option," he says.

They Shall Not Grow Old is Sir Peter's labour of love: he trawled through 100 hours of footage and 600 hours of audio to present the experience of World War I's Western Front, as lived by the men who were there.

"It takes quite a long time to listen to 600 hours of audio, I discovered," he says.

Sir Peter used state of the art technology to sharpen and colourise the archived vision, before converting it to stereoscopic 3D - turning century-old grainy and juddering footage into something that looks like it was shot today.

"The real hard work was restoring the black and white, from bad black and white to good black and white. It's actually way more difficult than going from black and white to colour."

Narrated by 114 different soldiers, the film takes the faces and voices of men long dead, and brings them back to life.

"You want it to be just about the guys and their experiences - you don't want to impose anything on it that's going to detract," he says.

"So you start at the beginning of the war, go through and finish at the end, and tell the human experience - not the politics or the tactics."

That human experience and realism means it doesn't shy away from horrors like latrines, trench foot, and gunshot wounds - but to his surprise and admiration, Sir Peter found the soldiers to be completely pragmatic.

"They don't want our sympathy; they weren't being emotional, hoping we feel sorry for them," he explains.

Despite there being many aspects of the war contained in the archives, Sir Peter decided to focus on just the experience of the British soldiers on the Western Front.

"There's so many aspects of the First World War that need to be told, it would be a 12-hour movie. Not that I'm against making 12-hour films of course, but we didn't have the budget for that, so we had to drill down on one specific area," he says.

Even with the deadline looming, he was still making alterations.

"I think it jumped from being 60 minutes to 90 minutes in the last two weeks before we finished it, which took everyone by surprise. But it just demanded it."

They Shall Not Grow Old will screen in cinemas around New Zealand on Sunday, Armistice Day, marking 100 years since the war's end.

Beyond that, Sir Peter hopes it's studied for generations to come: copies have already been distributed to every school in the UK.