Under Armour's inspiring 'Rule Yourself' campaign, featuring Misty Copeland, Stephen Curry, and Jordan Spieth, and produced in collaboration with Droga5 and director Wally Pfister, features an army of athletes training. But there wasn't enough time or resources to film hundreds of people. So how did they pull it off?

In a new video, production company The Mill shows how its employees cloned the athletes with plates, clever camera usage, and VFX.

To create the crowd of people, the company first rigged a five-camera array that maximized the number of plates they could shoot. While setting up, they had to ensure the cameras were evenly spaced and that the plates didn't overlap. Once they had cast extras who could perform the athletic drills necessary for the shoot, The Mill matched the extras' skin tone and hair to the athlete they wanted to duplicate.

Then, the company created identical clones of the featured athletes, scanning them head to toe to make CG agents. They used motion capture to ensure that the models' movements looked natural. Using various keying technologies and rotoscoping, The Mill then extracted the athletes from their original backgrounds. Finally, matte paintings were created by extending the environments shot in-camera.

As the company details in the video, because the shoot took place during a small window of time, it was nearly impossible to create uniform lighting conditions throughout each spot. To correct this, they replaced all of the skies, individually color-corrected each of the plates of the athletes, and manually added shadows.