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'Stealth': Keeping Speed With Jet-Fast F/X

Alain Bielik speaks with Digital Domain and visual effects supervisor Joel Hynek about bringing the fast-paced action of Stealth to the big screen.

Digital Domains work entailed designing and building futuristic stealth fighter planes, and developing a cost-effective and versatile technique to generate backgrounds for the many aerial shots. All images © Sony Pictures. Courtesy of Digi

Is it the exhilaration of flying at Mach 2? Is the uniform? Is it the excitement of air combat? Movies based on the deeds of air pilots have always been a favorite among moviegoers. From Firefox (1982) to Top Gun (1987) to Pearl Harbor (2001), those movies have also been a showcase for the very best special effects of their time. When Rob Cohen embarked upon directing Stealth right after finishing XXX (2002), he turned once again to Digital Domain and visual effects supervisor Joel Hynek, Academy Award winner for What Dreams May Come (1998). He needed the digital studios assistance to help sell the movie.

The script by W.D. Richter confronts an elite unit of stealth fighter pilots to their worst nightmare: their own replacement! In order to eliminate the risk of having a pilot shot down behind enemy lines, the U.S. Navy has developed a fighter jet piloted by artificial intelligence. However, when the computer develops a mind of its own, the human pilots must try to stop it before it provokes a war Ive been a pilot for more than 30 years, Hynek says. So, this was a very exciting project to work on. The first thing we did was to create a video test of 40 seconds to demonstrate what the airplanes would look like, what the style would be and the type of camera moves that we would try to achieve. After the studio had seen this test footage, the movie got greenlit.

A pilot for more than 30 years, visual effects supervisor Joel Hynek was the perfect choice to work on Stealth.

Crafting State-of-the Art Fighter Jets

Digital Domain embarked on two parallel efforts. The first one was designing and building two different kinds of futuristic stealth fighter planes; the second one was developing a cost-effective and versatile technique to generate backgrounds for the many aerial shots. The general look of the airplanes was conceived by two engineers from Northrop Grumman and refined by production designer J. Michael Riva. The human-piloted Talon jets were given a sleek, powerful and elegant look while the computer-controlled EDI was designed as a much more threatening aircraft.

Once the designs were approved, the planes were realized using four different techniques. Shots featuring the actors in and around the airplanes on the ground were photographed with full-size practical models. Special effects coordinator John Frazier also built a full-size cockpit and nose mock-up that was mounted on a pneumatic-driven gimbal in front of a bluescreen. The computerized set piece was used for tight shots featuring the characters in flight. Whenever a scene required the destruction of an airplane, 1/8-scale models were built by visual effects miniature supervisor Alan Faucher and photographed by Erik Nash. However, the majority of the shots feature a completely digital version of the Talon jets and EDI.

The CG jets were modeled in Maya and rendered in RenderMan, explains Markus Kurtz who co-supervised the CG department with Vernon Wilbert Jr. Joel had gathered an extensive library of airplane photographs and he kept referring to them, pointing out to the highlights on a surface, the color temperature on a wing. The quality of the lighting was paramount to the realism of the CG airplanes. We thus took 360° photographs of each location and mapped them inside a CG sphere in order to produce an exact reproduction of the lighting conditions on the digital planes. When there was no real location, we used our terrain generator, Terragen, to create a similar sphere that was, this time, entirely built from digital data.

The CG jets were modeled in Maya and rendered in RenderMan and then mapped inside a CG sphere.

Landscape Generator

Created by Matt Fairclough, Terragen had been in development at Digital Domain for several years. When Stealth got greenlit, it was considered a perfect opportunity to put the R&D project into actual production. CG terrain lead Brad Herman and his crew of developers really pushed Terragen very far, Hynek notes. The need for a landscape generator came from the main problem of visual effects, which is to combine a foreground and a background. In terms of light, contrast, perspective and movement, the foreground must be conformed to the background. On Stealth, we had so many aerial shots moving at such high speed that we would have felt very limited, had we solely relied on aerial footage. By creating the landscapes in the computer, we gained complete freedom in the way we designed our shots. We had the luxury of shooting our foreground first, with any kind of camera moves, and then only, take care of the background. As a visual effects supervisor, I had always shot the background element first. So, it was really wonderful to be able to work the other way around!

Working from datasets of elevations acquired on the Internet, the CG crew used Terragen to create the basic 3D geometry of the landscape. The elevations provided an average resolution of 30 meters per pixel, which meant that a 1,000x1,000 pixels map represented a terrain of 30 km2. With this data, there was not enough detail to reproduce the water and the wind erosion, Kurtz remarks. This was added procedurally via shaders. Sometimes, the Terragen landscape derived from actual elevations didnt work for the need of a specific shot or scene. When this happened, we were able to manipulate the data as much as we needed to and even add our own geometry. This new data was then rendered with the Terragen data as one landscape. Also, the program has a built-in render that allows you to create power-of-ten type of shots very simply. As you push in, the program keeps subdividing the surface by adding extra triangles in the geometry. You never run out of details! There is no other software that can handle that: with normal packages, you need an extremely high-resolution image or a series of images. Terragen starts from the geometry itself. In my opinion, the biggest advantage of the software lays in its ability to create photoreal atmospherics: the haze in the distance, the colors shift on the horizon, etc. The program is capable of computing the light really accurately. Rendering a terrain is only half the problem; the real issue comes from rendering the haze, the light, and the atmospherics. Once you have the landscape and the position of the sun, Terragen figures out what the atmospherics look like.

To solve the problem of combining foreground with background, Digital Domain developed Terragen, a terrain generator. When Stealth got greenlit, it was the perfect opportunity to put the R&D project into actual production.

Cloudy Weather

The other great challenge of the aerial shots was to create cloud formations. Rob Cohen insisted on layering every shot into a foreground, a midground and a background, Hynek recalls. He wanted to create an extreme sense of speed by getting parallax changes between layers. Although I had shot tons of aerial footage, we set out to model our own clouds using STORM, Digital Domains proprietary volumetric render built in Houdini. It gave us a complete control over the dynamics of the shots and the feel of speed.

Given the speed at which the planes were traveling, Kurtzs crew had to create tens of kilometers of digital skies, which presented a severe problem of data management: A sky that measured 60 km2 represented 100GB of volumetric data! We really worked hard on how to handle this enormous amount of data. What we eventually did was to build the sky into little boxes that each contained a portion of that sky. At render time, the program calculated which box was needed for each frame and loaded it in the computation. It meant that, at any given point, we rendered only the portion of the sky that was visible from the camera point of view. To further reduce the amount of data, we used low-resolution clouds for the background, keeping the very high-resolution models for the foreground. The program then automatically switched from high-resolution models to low-resolution models as the clouds receded in the distance.

While the terrain generated in Terragen completely worked as a realistic landscape, it lacked familiar details to help the viewer get a sense of speed. It was very hard to figure out how close we were to the ground, Hynek recalls. There was often no sense of scale, which meant that there was no sense of speed either. We ended up adding a lot of trees, roads, houses and other familiar elements that the viewers could relate to. Once the size references were added in, the shots worked much better.

A great challenge of the aerial shots was to create cloud formations. To create the layering director Rob Cohen wanted, Digital Domain modeled its own clouds using STORM, its proprietary volumetric render built in Houdini.

The Big Bang

The most spectacular scene of the movie certainly is the implosion of a tall building housing a group of terrorists. Nicknamed The Big Suck by the crew, the scene features a missile hitting the top of the construction, crashing through its floors and detonating in the basement. The explosion generates a blast that takes the whole building down from the inside. The central element for the scene was a complex miniature set-up engineered by Alan Faucher and a crew of 20. The building was created in 1/12th scale as a 25-foot tall model that was mounted on a 25-foot tall support scaffolding. Built in layers and held in place by dozens of hinges, cables and latches, the model collapsed on cue in the most realistic manner. The building element was then combined with a plate of downtown Bangkok (as Rangoon) and enhanced with many CG additions: dust, debris, cracks, etc. All the compositing on the project was carried out in Digital Domains Nuke under Kelly Ports supervision.

After devoting two and-a-half years of his life to Stealth, Joel Hynek has already embarked on a new ambitious visual effects project with Rob Cohen. Stealth was the hardest work for the longest period of time that I have ever done in my life! Originally, our intention was to use Terragen for shots that couldnt be achieved with aerial footage, but once Rob saw what he could do with the software, he started wondering Wouldnt it be nice if we could do this kind of move in this shot? We then kept increasing the number of Terragen shots and ended up creating 80% of the aerial shots with the software. In the end, we produced about 700 shots, representing 50 minutes of screen time.

Alain Bielik is the founder and special effects editor of renowned effects magazine SFX, published in France since 1991. He also contributes to various French publications and occasionally to Cinéfex. He recently organized a major special effects exhibition that opened Feb. 20 at the Musée International de la Miniature in Lyon, France. Displays include original models and creatures from 2010 Odyssey Two, Independence Day, Ghostbusters, Cliffhanger, Alien Vs. Predator, Alien 3, Pitch Black and many more. The exhibition runs through Aug. 31.