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Issue: Volume 36 Issue 7: (Nov/Dec 2013)

Birds of a Feather

By: Karen Moltenbrey

When Reel FX Animation Studios, a longtime digital effects and animation service company, set out to become a creation company by making its first animated feature film, the studio immediately faced a huge challenge that would make the most experienced veterans pause: The majority of the movie’s characters are turkeys, which means feathers. Lots of feathers. And, as any artist can tell you, generating fur and feathers is not a task that particularly tickles one’s fancy.

JAKE’S FINAL GROOM contains more than 40 different feather clubs and well over two million individual hairs, or barbs.

But the work in Free Birds was made easier and the results spot on, thanks to a proprietary feathering system called Avian.

Free Birds, directed by Jimmy Hayward, tells the tale of two turkeys from different backgrounds – Reggie is a brainy free-range bird with a smooth silhouette and rough groom, while Jake is a rather large, factory-raised bird with more genetically infused brawn than brains. Both travel back in time to change the course of history so that their species is no longer the “guest of honor” during Thanksgiving.

“The first challenge was to make sure the audience would want to look at these birds for the length of a feature film. They had to be appealing, likable, and expressive,” says Hayward. “So, we veered away from reality when it came to character designs, but we went for realistic textures as much as possible.”

Keeping Reggie, Jake, and the flocks in fine feather was done with Avian, developed at Reel FX by TDs Harry Michalakeas and Tymon Pitts, along with Monika Sawyer, fur and feather supervisor. Sawyer had worked with Hayward on Horton Hears a Who! in a similar capacity with a fur system, and was brought onto the production to oversee the grooming process. The proprietary system enabled the artists to generate feathers of all sizes and shapes, and then groom the birds, viewing the results in real time within the Autodesk Maya viewport prior to rendering.

According to Pitts, the crew needed a good recipe, a system that was complex but could be used by the artists. “That was one of our goals, to make it artist-friendly, so you didn’t have to be a programmer to use it,” he says. Yet, the system had to be robust in order to handle the film’s nearly 100 characters that were created by a handful of artists. “We pulled people from different backgrounds, such as lighting, and they all used it,” Pitts adds, noting that the artists were trained and up and running in approximately three weeks, not three months, as can be the case with other fur and feather systems.

“We wanted it to be easy to use, and to do that, we needed control over the whole system,” adds Pitts, “that’s why we developed our own [tool].”

Avian took approximately a year to develop, and many of the features were devised on the fly, so to speak, as the need arose. During development, Michalakeas, Pitts, and Sawyer did a tremendous amount of physical and theoretical research, including examining a real turkey wing for the lay of the feathers and studying numerous SIGGRAPH papers, such as one from 1992 on retopologizing polygons that helped formulate the feather placement process (Greg Turk’s “Re-Tiling Polygonal Surfaces,” 1992). “We looked at what others had done, how Weta did some of the feathers for The Lord of the Rings movies and what Blue Sky did for Rio. Monika was one of the fur artists who worked on Rio, so we were able to draw on her experience from that, as well,” says Pitts. “We got different ideas from many sources and came up with our own ideas, too; and, in the end, it resulted in a pretty good system, in my opinion.”

Feathering Process

Reggie served as the hero model, and the resulting technical development was used to drive the other turkeys. Because Jake’s features are more defined than Reggie’s, he required some further development. Once the models were made in Maya, they were sent to grooming, where the group carved the models into various sections (body, arms, head, and so forth), and added feather nodes on each section. Jake, for instance, had 10 to 12 different node systems on his main body that gave him his distinct look with extensive pecs and glutes, while Reggie’s body had just one system for his skinnier frame.

The wing feathers were placed in distinct rows, prompting development of a growth curve system. For the rest of the body, though, the feathers were placed procedurally, so they appear random – “evenly spaced random,” Pitts says.

The artists used Avian to produce the contour feathers, which they applied to the body. There were flight feathers as well, driven by a NURBS surface that the animation department rigged and controlled. “We placed them all over the body and the feathers would interpolate the differently shaped surfaces,” says Pitts. “Avian is unique in that it is not an instancing system. It’s more that each shape is interpolated to get the final feather shape.”

In most bird movies, like Rio, the feathers look more like fur, and it’s hard to see the O shapes. In these instances, the artists use little fly-outs here and there to give the illusion of feathers. But for Free Birds, the art required the feathers to be distinct, like little shingles. “The problem with distinct feathers is that you see the penetration a lot easier,” says Pitts.

Indeed, the artists had to contend with the constant colliding and stretching whenever the turkeys moved. Initially, they devised a plan that involved solving for a simulation, but after a long, painful process, they changed directions and instead of trying to fix the problem, developed a system that would prevent the colliding in the first place. Called Aim Mesh, the solution essentially placed a polygon cage over the Avian feather system to drive the orientation of the feathers. Animation would then rig up the Aim Mesh so when there was squashing of the body, such as when a turkey lifted its leg, rather than have penetration, custom deformers on the Aim Mesh would simply pull up the mesh.

“It prevented 99 percent of our collision right off the bat; the remaining 1 percent that was colliding was barely visible, so we just let that go,” says Pitts.

The crew exported all the feathers to an Alembic format read by a Pixar RenderMan procedural, which converted the information into RI curves for rendering. A shader, developed by Marlin Rowley, enabled the group to pull surface information from polygon representations of the feathers – a smooth normal from the polygon mesh – and apply that to the barbs of the feathers for smooth shading across the entire feather.

Artists at Reel FX devised a feathering system, called Avian, for Reggie, Jake, and the rest of the flock.

Grasping the Concept

In Free Birds, the turkeys often use their wings as hands, so the feathers had to act sort of like fingers. “If you look at all the animated movies that have been made with birds in them, the characters either have wings that aren’t really used as hands, or they have hands that are not wings. We have characters whose wings are used as hands, so the challenge with that was getting enough strength out of the fingers, even though they were made of just feathers,” Pitts explains.

With help from Tom Jordan, modeling supervisor, the crew devised a feather-stacking solution, as bunches of feathers were stacked atop one another, with the thickness controlled by animation. So, in scenes where they needed strength out of the fingers, the group would bump up the number of stacks and the thickness, but in scenes where the fingers needed to be feathers, they would turn the system way down and it would look like all the other flight feathers on the turkeys.

“The animators needed the freedom to make the birds do whatever they wanted because sometimes they were doing bird things and other times human things, and the system had to support both,” says Pitts.

On average, there are 11 turkeys per shot in the film, although some scenes had upward of 50 feathered characters. In one scene, 1,241 turkeys are visible. To keep rendering manageable, the crew employed some tricks to help cut back on the data crunching – for instance, some of the background birds had rendered polygon representations of feathers rather than actual feathers. Nevertheless, there were usually millions of feathers on the screen at any one time: Reggie alone has 6.2 million hairs, or barbs, while Jake sports 2.2 million, which translates into 5,086 feathers – slightly more than a real turkey, which averages 3,500 feathers.

But, real turkeys can’t trot the line between human and avian behavior, nor can they change history as Reggie and Jake attempt to do. And, perhaps best of all, real turkeys don’t have the personality to pull off a starring role in a comical, time-traveling animated feature film that’s a visual feast for audiences – particularly vegetarians. 

Karen Moltenbrey is the chief editor of CGW.

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