When Britain’s Imperial War Museum went looking for a motivated movie director to dust off and spruce up some of its World War I footage for a documentary marking the 100th anniversary of the war’s end, it found an eager and worthy partner in Peter Jackson.

The Lord of the Rings trilogy director and Oscar winner is known for his Gandalfian wizardry with the technical aspects of cinema, and Jackson came preloaded with an abiding interest in the war.

In part because he owes his life to it — his British grandfather fought in World War I, and talked so glowingly of his New Zealand comrades that Jackson’s dad decided to move there, and start a family.

Jackson heard war stories growing up, became a buff, and jumped at the chance to make what would become They Shall Not Grow Old, to be released theatrically on Feb. 1. It previously had a limited “special event” run in selected theaters, but it proved to be more popular for one-off screenings to accommodate. (It has already made $8.3 million.)

Jackson began his work on the project five years ago and in that time he found his enthusiasm tested by the serious challenges of transforming the near-ruined War Museum footage into something that would engage the modern eye, and thus the imagination.

The film, which had often been copied over the years, was washed out or darkened, and even the good stuff — shot on hand-cranked cameras — ran at random, obsolete speeds that gave the footage an outdated and alienating look.

“When you looked at it,” Jackson said, “it suggested a historical distance that translated to an emotional barrier. And we wanted to remove all barriers between [the contemporary viewer] and the actual soldiers. We wanted to strip away that distance that you feel when you look at the herky-jerky old footage.”

So he and his team looked for ways to upgrade sounds, film speeds, and color that would make the images — especially the movement of the human figures — resonate with contemporary audiences.

The challenge was technical, but also ethical – he wanted to colorize the images, and that meant confronting bias among those who associate the process with the degrading and altering of classic Hollywood film. His approach also raised questions relevant to the documentary form: If you’re altering documentary footage, are you really making a documentary?

Jackson looked at it another way. He considered the mandate of the original photographers — to capture the physical reality of life at the front — and set out to use modern technology to meet that mandate in ways unavailable a century ago.

“These guys were not directors as we think of them today," Jackson said. "They were not DPs [directors of photography]. They were government employees at the front with cameras and simply there to record what was going on. They weren’t making an artistic choice between, say, black and white and color. Black and white was what they had. We took the attitude that if their job was to record the daily life of the soldier as much as possible, then it’s right to acknowledge that daily life was full of color.”

Getting the right color was important. Jackson traveled to France, visiting locations — often exact locations — he knew to be featured on the old footage, and shot thousands of photos. Those colors — of the grass, flowers, earth, trees, rocks — were incorporated into They Shall Not Grow Old, to the extent that the budget would allow.

The film features 300 colorized shots, enough for about half the movie’s running time. and opens with a long section of cropped, unimproved old footage of recruitment, training, and transport across the channel. The film springs startlingly to life once the fighting starts in France, and Jackson starts to use the upgraded material.

The before-and-after contrast functions as a shrewd way of demonstrating the value of Jackson’s approach, though the director said he wasn’t thinking in those terms when assembling They Shall Not Grow Old.

“I wish I could take credit for making that artistic decision," he said. "But it was mostly about what we could afford. The budget covered so much, and more of the story needed to be told. So that’s what dictated the approach.”

Jackson dug into his own pocket — he won’t say how much — to pay for colorization of elements he thought needed to be emphasized. This included gruesome images of the frostbite, gangrene, and “trench foot” suffered by the soldiers, grisly details that drive home the reality of the daily life of the common soldier, which emerged as the movie’s theme. (There’s a reason the movie is rated R.)

“This was born out of the 600 hours of audio and 200 different [veterans]," Jackson said. “These were not politicians or generals. These were soldiers. None of these guys knew what was actually happening in the greater view of the war. They didn’t understand the strategy or the politics. They were told what to do, and they only knew what they saw just to their left, or to their right. So that became the movie. Their experiences, the intimate story of that experience.”

Jackson’s team cleaned up the audio, hired lip readers to deduce what the soldiers were saying, used actors to provide voices in certain scenes. They recorded the sounds of vintage weapons, vintage bullets hitting sandbags, period howitzers firing shells. One incredible bit of footage shows a shell bursting in midair, sending a shower of projectiles toward the ground below, raking the surface of the earth with alarming effectiveness.

Combat footage was hard to come by — footage of death not so much, and the macabre scenes in They Shall Not Grow Old reinforce the war’s awful reality.

Jackson, though, was really thinking of ways to make the soldiers live again. The hardest part was syncing up the old footage and its outdated frame rates with modern 24-frame-per-second projection speeds. Silent-era footage is supposed to run at 16 frames per second, but Jackson found the hand-cranked footage he worked with varied — from 10 to 18 fps. His artists made digital copies and brought everything to 24 fps by inserting new frames into old footage, borrowing digital information from the frames on either side of the inserted frame.

The effect is amazing. It’s the speed, as much as anything else, that shows the men as the young, agile, full-of-physical-prowess people that they were.

I used the term athletic, and mentioned to Jackson that it would be interesting to see his techniques applied to footage of old sports figures, whose movements often look comically out of date. To see upgraded footage of a young Jazz Age Babe Ruth, for instance, taking a home-run cut, and compare it with the stars of today.

“I hope that’s what happens," Jackson said. “I hope that archives around the world see this film, and think about using this kind of technology so that people can really look at these important images with new eyes, to take some of this stuff from the teens and ’20s, and upgrade them to be able to see these events as you would have if you were there at the time. I think it’s an incredible new opportunity."