ByElise Jost, writer at
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Elise Jost

If there's one painstaking task that's always existed in the world of animation, it's rendering hair. Considering that the average human head holds about 100,000 hairs and that the slightest gust can move every single one of them, how is it possible to draw and animate realistic hair on screen?

It gets worse when you decide to do an animated movie with animals, which are basically covered in hair. For the first time since Bolt (2008), Disney Animation has created a movie where not only the lead character is a furry critter, but all of them are. In Zootopia, the giraffe has more strands of hair than every character in Frozen combined, and that proved to be a substantial challenge.

The Challenges Of Computer-Animated Hair

Long gone are the days when Disney animators drew every single frame by hand. Look at Cinderella's hair: it's every girl's dream hair because it looks so soft and fuzz free, but it might as well be pizza dough.

Animation Studios Innovate Every Year

Ever since animation involved computers and innovation wasn't just a matter of inventing quicker ways to draw, the number of tools for making hair look more realistic has increased exponentially. Animation studios have their own development teams that keep pushing the boundaries of what is technically possible.

But pizza dough is so much easier to comb!
But pizza dough is so much easier to comb!

Disney Pixar's Brave (2012) set a significant milestone for computer-generated tresses with the use of a simulator named Taz. To give Merida's curly bonce that bounciness, it started off with cylinders around which the curls are wrapped, allowing them to stretch and snap back into place. In total, 1,500 handmade strands were placed on Merida's head. Back then, Taz was a CGI revolution.

Jump forward one year and you get Frozen (2013), in which heroine Elsa boasts 400,000 strands of hair on her head. Now if you look at Zootopia, you need to know that the movie features 64 different animal species, from which the creators drew about 800,000 different character models. For example: baby mouse, bigger baby mouse, grandpa mouse, funny uncle mouse, etc. And one mouse has 480,000 hairs alone.

Meanwhile, the giraffe's body in Zootopia is covered in 9 million individual hairs.

Inventing New Tools For 'Zootopia's' Furry Heroes

In order to avoid having to move these millions of strands individually, the team behind Zootopia created a fur shader; a tool that would allow them to brush multiple hairs at a time. On top of that, a process called path tracing controled how the light bounced off the hairs, resulting in different textures. To give the fur a realistic feel of weight and shape, the team also introduced PhysGrid, a type of software that maps the muscle and the fat below the hairs. Of course, that can mean hundreds of hours of rendering — for a single frame.

For producer Clark Spencer, animation is a real culture of innovation:

“When 'Snow White' was released, it really was a technical achievement. And it really is our goal, as a studio, each and every day, to push technology and innovation. 'Zootopia' follows in the footsteps of 'Tangled,' 'Wreck-It Ralph,' 'Frozen,' and we’re competitive. Each of us look at our films and say, ‘How do we go to that next level?’ And that’s really been an extraordinary journey for all of us in bringing this world to life.”

How To Create Gorgeous Landscapes

There, there... Only 3,000 hours of rendering left.
There, there... Only 3,000 hours of rendering left.

However, the studio couldn't stop there: Once you've got these insanely detailed characters, you need scenery that can claim the same level of lushness. What about the trees, for example? In Zootopia, forests and other types of vegetation were generated thanks to a tool called Bonsai, which makes it possible to copy and customize items very quickly. Although it wasn't required for the movie, Bonsai engineers were able to create 7.7 million trees in a single shot.

And Why Do We Need That, Again?

You might be wondering: Why put so much effort into such little details? The thing is, our brain won't notice a few thousand strands of extra hair, but it will react instantly if the movement or the light reflection just feels "wrong." Which means that rendering millions of strands isn't about getting you to whisper, "My, what a heavenly fur!" every time you see an animal on screen, it's about actually taking your mind off the fur to focus on the story. Obviously, it's also gorgeous, but what's most important if you want to enjoy the movie is this natural, realistic vibe.

Get Ready For The Release Of 'Zootopia' On March 4

Can't wait to go see Zootopia and bore your friends by blabbing on about what it takes to render sloth hairs? Well you're in luck, because the movie is scheduled for release on March 4.

Until then, (re)watch the trailer below:

Did you know that it takes so much work to animate a fluffy-looking rabbit?

Sources: io9, Wired


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