How 'Wolfwalkers' used 3D technology to transform 2.5D animation

• Animated films can be 2D or 3D, but oftentimes they're actually a bit of both.
• Animators use "2.5D" animation techniques to make flat images appear 3D and even mix 2D and 3D elements within the same film.
• There has been a lot of innovation in the 2.5D space with movies like Sony's "Spider-Man: Into the Spider-Verse," Disney's "Paperman," Netflix's "Klaus," and the Golden Globe-nominated Apple TV film "Wolfwalkers."
• "Wolfwalkers" used 3D models and virtual reality to help create immersive, hand-drawn images that let the viewer see through the eyes of a wolf.
• We spoke with Cartoon Saloon's Eimhin McNamara, who was tasked with helping create these scenes, to find out how they did it and why they chose to lean into hand-drawn animation over 3D CGI.

Following is the transcript of the video.

Narrator: This is 2D hand-drawn animation.

[horns toot]

And this is 3D computer-generated animation.

But many films actually fall somewhere in between -- or what's often referred to as "2.5D."

This is when a variety of techniques are used to make an otherwise flat 2D film feel 3D, with depth, but also with a unique hand-drawn style. Animators might use illustration tricks like shading, layering, forced perspective, and parallax on 2D objects to make them appear as if they existed in a 3D space.

Some films even mix dimensions by adding 3D characters and background objects to 2D films.

Disney's "Beauty and the Beast" was primarily in 2D, but the chandelier? A 3D CGI add-on. And animators created this jungle entirely in 3D, so a 2D hand-drawn Tarzan could swing through. "Lion King" was the same. This wildebeest stampede was digitally simulated in 3D, but Simba was in 2D.

[Simba gasps]

And animators are continuing to push 2.5D further, because there are still some things that computers can't fully replace, like the graphic look of comics in "Into the Spider-Verse," which incorporated 2D line work on 3D models.

The latest example of 2.5D innovation is Cartoon Saloon's 2020 film, "Wolfwalkers," which, like "Tarzan," created a 3D forest -- only this 3D forest would never actually appear in the final film. A team of nine animators would ultimately recreate every single digital frame of these scenes by hand on thousands of sheets of paper.

Eimhin McNamara: The idea was that it would not feel too clinical, too clean, too, like, artificial.

Narrator: That's Eimhin McNamara, whom directors Tomm Moore and Ross Stewart tasked with creating the "wolfvision" scenes for the film. In these scenes, the viewer sees everything through the eyes of the main character, Robyn, as she transforms into a wolf.

Eimhin: The main thing with the wolfvision that Tomm and Ross wanted to get on screen was they wanted to make it feel like a heightened perspective or a heightened experience, a heightened-reality version of the film.

Narrator: The animation team could've made a fully 3D film relying on digital technology, but they opted for 2D hand-drawn animation instead, specifically with graphite, to mimic art from the 1600s. But they decided to use 3D tools to first plan out the scenes. Using these tools and virtual reality in the previsualization stage helped create more realistic backdrops and mimic the natural movement of the wolf.

There were two main settings in the film, the town and the forest, both with their own wolfvision scenes and art styles. The town, with its woodblock print, was easily made with more traditional 2.5D techniques. Animators worked in After Effects to place elements at various distances from the camera, creating an illusion of depth.

This built on a technique that goes back to 1942, when Disney shot the opening scene of "Bambi" using a multiplane camera, which has layers of painted glass to achieve a similar parallax effect. But the forest previs scenes required a lot more innovation and a lot more work to get right.

They were inspired by the look and feel of the Studio Ghibli film "The Tale of Princess Kaguya," so these scenes required a more organic stroke with a flowy watercolor style, a creative choice you couldn't really get with CGI.

Eimhin started out with a simple hand-drawn sketch of the woods and a telescoping effect. He used depth maps and Photoshop to help create this illusion and sketch out the frames by hand one by one. But he quickly realized they would need a more dynamic camera, because the wolf wouldn't just be walking forward, it would also be jumping, looking around, and even bobbing its head as it panted and breathed.

Eimhin: It helps you feel like you're actually in, you know, the head of the character.

Narrator: So the team experimented with virtual reality using the headset Oculus Rift. They drew and built a 3D forest in VR with a sculpting program called Medium.

This virtual set was then transferred to a computer-animation tool Blender, where artists painted on more stylistic 2D elements. Animators used these rough overlays to adjust and refine the 3D model.

Eimhin: You would basically draw on top of the 3D models. Bake in some line work onto the forms. Would still give it kind of a nice kind of squiggly and kind of hand-drawn feel.

Narrator: Other 2D elements included soldiers and rough flames for the forest-fire scene. That way, animators wouldn't have to guess locations for those assets later on. This 3D model was used to block out the path and speed of the camera movements.

Eimhin: And we would then start moving the camera through it, bring it to the directors, go, "OK, well, how's the movement here? Is it looking good?" They might go, "Actually, we should probably go a bit slower with this so it has a bit more, like, oomph." Or, "We should go faster." Whatever the case may be.

Narrator: Now, Disney used a similar method back in 1999, when animators created a 3D forest for a 2D Tarzan to swing through using a program called Deep Canvas. But they ultimately kept the 3D model and used digital paint in the final film.

For "Wolfwalkers," the audience never actually sees this 3D model or all the intricate design work involved in creating it. The final images were all eventually covered in handmade graphite drawings.

Eimhin: It's not just about concealing 3D, it's more about, like, how can we build on it and make it so it is primarily 2D?

Narrator: Eimhin printed out each frame of his 3D sequence on paper using red ink as a guide. Then a team of nine animators drew directly over each of these red images by hand with charcoal and pencil. The bright red could easily be removed later from the blacks and grays in the digital-clean-up stage.

Drawing each frame by hand is a time-consuming process, so to help manage the workload, they decided to halve the number of images by playing with the frame rate. Normally, you'd see 24 different images every second, but here they drop down to 12. That way they only had to draw 12 images for every second of the scene.

But changing the frame rate can also make the scene appear choppy.

Eimhin: So, we kind of compensated for that by smudging things and actually using the organic qualities, so it is just more like a drawing than it is like a camera movement.

Narrator: Smudging was also used to create motion blur, like in this kitchen scene with the checkered floor. And the hand-drawn style allowed them to get creative with certain elements, like the smoke of the fire.

Eimhin: So, the graphite would bleed out. It would go to the white of the page towards where the fire was, so you would get a nice kind of flickery feeling of the fire, like almost burning up the charcoal or such on the paper.

Narrator: Once all of the drawings were complete, they scanned the approximate 6,000 hand-drawn images, digitally removed the red lines, and touched up the line work. They also added additional layers in the composite stage.

As you can see here in this town scene, the various tones and textures and the colored wolf scent are all drawn separately. These multiple layers meant much more paper.

For example, this scene, when Robyn wakes up as a wolf for the first time, required about 1,500 printed pages. The result of all this hard work was an innovative 2.5D style that highlights the artists' skills in drawing by hand -- something a computer alone wouldn't be able to do.

Eimhin: It's, again, just about getting an organic thing on screen that looks like people made it versus, you know, computer hit render.