Issue: Volume 37 Issue 3: (May/Jun 2014)

Birds of Paradise

By: Karen Moltenbrey

The story is epic and centuries old. Noah is forewarned that a Great Flood is coming and will wipe out mankind. He is then instructed to build an ark and usher aboard breeding pairs of animals and birds so that life can begin anew after the deluge. The feat required to bring Director Darren Aronofsky's vision of this biblical tale to the big screen required cutting-edge digital technology, particularly when it came to the flood and the animals and birds.

ILM handled the digital animals and water, while Look Effects created the effects for the Garden of Eden sequence, including a matte painting of the Tree of Knowledge, the apple, the serpent, and all the birds. Thousands and thousands in a multitude of species. Large birds, small birds. Birds of prey, birds of peace. Individual birds, flocks of birds. And, feathers. Lots of feathers.

In fact, every bird in Noah is digital except for two doves and a raven. To handle the work, Look devised two major systems from the ground up: one for feathering and another for flocking.

The biggest challenge was designing the birds so they would generate enough volume to make it appear as if Noah had collected two of every bird on Earth. The artists started with a few hero birds and built 14 different body types. From each of those, they created a number of unique grooms.

LOOK EFFECTS CREATED custom feathering and flocking systems for the birds in Noah.

"By varying overall color and size, we were able to give the impression of a tremendous amount of diversity from a relatively small number of base birds," says Dan Schrecker, VFX supervisor. 

For shots with more distant birds, the team used its flocking system, which enabled the artists to populate scenes with as many as two million birds. As the camera gets closer, they hand-animated hero birds. All told, the animators worked on over 3,000 individual, hand-animated birds, starting with key ranges of motion that were fed into the flocking system. These then served as a starting point for the hand-animated hero birds.

A key aspect of the bird work was Look's use of Deep compositing. Used for the first time on a large scale for the live-action VFX film Rise of the Planet of the Apes by Weta, Deep allows compositors to work in 3D space in a way that provides added flexibility and functionality that would not be available in a normal 2D compositing approach. "Simply put, without our use of Deep compositing, we would not have been able to do this work," says Dave Zeevalk, 3D supervisor. "It was the basis of how we put together our most complex shots and was one of the first decisions we made. Going forward, it made the bulk of our task easier, especially later in the process when changes that might have otherwise been major were handled more easily due to this approach."

A good example of how this was invaluable can be seen in Look's biggest shot in the film, in which Noah and his family walk down the aisles of bird roosts and put the flock to sleep with their magic smoke. Because of the overlapping nature of the bird roosts and the more than 1,800 hand-animated hero birds, the artists needed to find a way to put it all together, while maintaining flexibility throughout the process.

"As the camera dollies across the set and the birds fall asleep in their roosts, we were faced with the challenge of how to properly seat our digital birds into the practical set. Because they were essentially crisscrossing each other during the course of the shot such that a single bird would appear in front of and behind other birds and the practical set, standard holdouts were impossible," says Zeevalk. "We relied on Deep techniques to combine the CG elements with the roto mattes that were required for the practical roosts. This allowed us to do things like pull individual birds out of the comp fairly late in the process, stay flexible with color and depth of field without introducing edge issues, and deal with the semi-transparent curtains that were present in the practical set."

In addition, the artists rendered the elements with full Deep RGB and breakout passes. Normally, the approach is to render Deep opacity and shadow maps because there is less data to manage, and in most scenarios, this is enough, Zeevalk explains. But because of the volume of birds and the amount of flexibility needed, the group took a more extensive approach. "This led to huge amounts of data that we had to manage, but in the end enabled us to achieve what we set out to do," he adds.

Birds of a Feather

Because of the large variety and volume needed, as well as the required efficiency, the Look team opted to build its own feathering system, which comprised a feather creation tool, a grooming tool, and a deployer.

"Early on, we realized that we couldn't use a traditional hair or fur system because of the randomness with which points were distributed across a surface," explains Zeevalk. "Due to the fact that the layout of feathers across a bird is not completely random, as hair is, we looked for other ways to apply our feathers."

The artists ultimately adopted a blue-noise pattern as a basis for their distribution, whereby every point on a surface has a scale that represents the scale of that feather, and its distance to its surrounding neighbor feathers is based off that scale. They then wrote a blue-noise solver that would apply those points on a surface and then resolve spacing issues. Multiple techniques were used to instance those feathers.

The feathers themselves were a series of cards that were created using a photoreal feather-creation tool built in-house. This separate application allowed them to define shape, length, and other attributes, starting with a flat, oval-shaped, low-resolution feather. They were able to push points around until they were happy with the general shape of the envelope, at which point the tool would generate the rachis along the spine of the envelope and spawn hundreds of curves to represent the barbs. The artist had fine-grain control over splitting, curl, noise, and all the other various attributes that define the look of a realistic feather. The end result was then made into a texture to speed up rendering, as there were too many birds to directly render the curves of every feather.

THE USE OF DEEP COMPOSITING enabled Look Effects to work in 3D space and was crucial  to completing the work.

For grooming, the artists interactively painted maps on the birds, which enabled them to control a wide range of feather attributes, including scale, base color, tip color, lift (how much a feather lifts off the body), and which feather types to use. The groomers did not have to generate every single feather, and instead relied on the grooming tool to instance and blend them together into the desired effect.

Another tool allowed the artists to draw in areas of finer detail. "For instance, in the areas surrounding a bird's eye, we need a higher density of feathers, and this tool allowed us to achieve that without increasing the resolution of the underlying geometry," says Zeevalk. "A separate tool allowed us to control basic feather direction with a few pen strokes, instead of having to hand-comb each feather."

A final piece of the puzzle was the deployer, a multi-faceted tool for distributing and applying grooms and feathers within each shot. On a macro flock level, the deployer decided which birds received which grooms.

"With our volume of birds, we wanted a way to procedurally assign grooms to individual birds, so our system looked at what types of birds existed in a given shot and programmatically dispersed grooms, taking note of which birds were in proximity so we didn't end up with two similar birds butting up against one another," explains Zeevalk.

Digging deeper down to the feather level, the deployer took each groom, which was initially designed in a rest position, and applied it to the animated birds, recalculating feather positions frame by frame to maintain relative angles from one feather to the next. "The idea here was that because of the high volume of birds, we couldn't solve for collisions between individual feathers. Looking at averages, the deployer detected outliers and brought those feathers in line with the others surrounding it," says Zeevalk. "This was essentially a method of avoiding most collisions, when a true collision detection system was out of reach for the scale on which we were working."

The deployer also handled the caching of feather geometry, which was then instanced at render time, communicating with Side Effects' Houdini to define exactly what needed rendering -
that is, avoiding feathers that weren't visible to camera - and applying static and dynamic noise to feathers for ruffling and air resistance as the birds flew.

Part of the Flock

The second major system Look built was a flocking system. The group started with a series of loopable animation cycles and progressed to different ranges of motion, building a library to draw from.  

Because there were a number of shots that required flocking, the group created multiple ways to generate a flock. For shots outside the ark, they were able to work more loosely, generally using curves to drive direction. Inside the ark, they followed a 3D volumetric approach using the geometry of the interior to confine the movement of the flocking birds. The system would then choose which animation cycle to use and when to transition - based on a bird's motion in the world. To prevent collisions, each bird had a field of view of close to 120 degrees. Anything outside of that range was ignored, and as the birds moved around and past one another, their flight paths were constantly updated and re-calculated based on what they "saw" in front of them.

"This flocking AI was the backbone of our system," says Zeevalk.

Birds were then instanced to create the full count needed for each shot. In addition, every bird would spawn a mate, and these would stay in close proximity in order to fly two-by-two as required by the story.

Another key piece of the system gave the appearance of feathers, without the added data of actually feathering all the flocking birds. The artists generated shaders based on each of the grooms and applied it to the flocking birds. "This made them appear consistent with our hero birds but saved us a lot of processing that we didn't have to do because of their distance from camera," Zeevalk explains.

The role a dove plays in the biblical tale is significant, as was Look Effects' role in the film's visual effects.

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