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Issue: Volume: 27 Issue: 5 (May 2004)

The Alamo Rerendered


On February 23, 1836, some 180 people—Americans who had settled in a northern part of Mexico called Texas, as well as the Tijanos who lived there, and a group of cavalry men—prepared to defend a fort called the Alamo from attack by Mexican forces. The rebel army had captured the fort from Mexican General Marin Perfecto de Cos the December before. But this time, Mexican General Antonio Lopez de Santa Anna arrived with an army of thousands, and on March 6, recaptured the Alamo, leaving all the defenders except women, children, and one slave dead. Within two months, on April 21, General Sam Houston led a surprise attack on Santa Anna and his forces. This time, the Texans won the battle and, with it, independence for the Republic of Texas. The battle cry, "Remember the Alamo!" echoes today.

In April, Buena Vista Films released the latest feature based on the historic battle and aftermath. Directed by John Lee Hancock, starring Dennis Quaid as General Sam Houston, Billy Bob Thornton as Davy Crockett, and Emilio Echevarría as General Antonio Lopez de Santa Anna, The Alamo attempts to stay true to history while honoring the legends.
For a scene in which Davy Crockett takes a bow on stage during a play about him, Matte World Digital replicated the audience (top) to create a full house and removed modern-day artifacts to create the final shot (bottom).




Although visual effects play a role, you won't see them—or at least you won't if the effects are successful. "This is not a visual effects show per se," says Craig Barron, visual effects supervisor at Matte World Digital. "But innovative effects are happening all through the film. We hope the audience just figures we shot everything for real."

Much of the filming took place on a massive set built on a ranch outside Austin, Texas, where a village representing San Antonio de Bexar was constructed. Slightly outside the village—and the set—was the Alamo, a mission fort.

Often Matte World Digital would sweeten shots of Bexar and of the Alamo, adding emotion to a shot by painting clouds in the sky, even changing the moon to the historically correct phase in a night shot of Bexar. "This was a first," says Paul Rivera, chief technical artist.

Using Adobe's Photoshop and Alias's Composer, the crew modified a theater in which Davy Crockett appears. "We made the interior smaller, removed the art deco elements, exit signs, wheelchair ramps, and everything else that would not have existed in 1836," says Barron. The audience was composited from multiple passes of 200 costumed extras who switched seats for each shot. But these typical fix-it-in-post shots were not typical of the work done at Matte World Digital for this show.

Sent by Sam Houston, Colonel Jim Bowie (Jason Patric) and 25 men arrived in San Antonio on January 19; Lieutenant Colonel William Travis (Patrick Wilson) and his company of 30 arrived February 3, not expecting Santa Anna to show up before spring. But when Davy Crockett showed up on February 8 with 12 Tennessee Mounted Volunteers, they were chased into town by the Mexican army, which was gathering on the outskirts of town. Santa Anna had mercilessly marched his troops some 350 miles from Saltillo through the mountains of northern Mexico, through rain, snow, and ice, to San Antonio.

The march was shot in Austin with 236 men dressed in Mexican military costumes traversing open fields dusted with artificial snow. It would be up to Matte World Digital to convert the open, sunny landscape into a wintry march through the mountains.
Six-foot-tall tracking markers set along the rail (top) helped Matte World artists derive the camera move and assemble 12 shots of groups of soldiers into the final shot (bottom).




The studio created the terrain with Discreet's 3ds max using data from Camera Control's Milo motion-control camera and then projected textures painted by digital matte artist Chris Stoski onto the landscape seen by the virtual camera. The soldiers were rotoscoped out of the live-action plate using Pinnacle System's Commotion and added to the terrain. The snow, created with max particles, was rendered in layers. "We had more than 10 levels of snow," says Rivera, "from blowing snow in the foreground to a haze in the distance." The compositors used cues from live-action elements to know where and when to place flurries of snow in the foreground; motion blur was added in compositing. "We'd bring in the snow in the right ratio to a blowing flag," says Rivera. "Advance planning helped us put the shot together quickly."

On February 23, Santa Anna reclaimed San Antonio. For the dramatic scene of General Santa Anna riding through the square with his generals past thousands of his troops, Matte World Digital needed to create thousands of soldiers standing at review from groups of 200. First, the effects crew shot the riders trotting through the empty square. Then, 12 sets of the groups were filmed with a static camera in different sections of the square. "We check-ed with the historian on location and found out that the Mexicans didn't salute," says Glenn Cotter, 3D artist. "But, it was important that they not look like static elements, like we painted them in. We wanted to have some movement among the troops standing at attention, so as Santa Anna rides by, we had them shoulder rifles, present arms."

The 12 sets of 200 troops were then assembled so that it looked like Santa Anna was riding past them. "Because the riders were shot with a camera that panned but did not move through space, there's no parallax," says Cotter. "So, we could project the individual groups on the inside of a sphere." The live-action camera was tracked, and that movement was matched with a CG camera that panned across the images of the troops assembled on the inside of the sphere. In addition, compositors added clouds to the shot.
To create a mountainous landscape, the crew applied texture maps to a terrain modeled in 3ds max (top). The troops were then composited into the CG landscape (bottom).




That night, the siege began. Inside the Alamo, Davy Crockett played his fiddle to inspire the Alamo defenders. Only a short distance away the Mexican army surrounded the Alamo and prepared to pound the fort with cannon and rifle fire. To add drama to the shot, Matte World Digital repainted the sky with a sunset, and added fires, torches, troops, and firelight on the buildings.

Before dawn on March 6, waves of Santa Anna's troops began attacking the Alamo. At Matte World Digital, several artists in the studio worked on shots for the sequence—some taking shots early in the battle, others the later shots—replicating troops, adding gunfire and flares. One far background was painted by Chris Evans, another was painted by Scott Brisbane. For fallen soldiers in the foreground, the crew added photographs of themselves wearing Mexican uniforms.

Compositing was handled by Todd R. Smith, technical artist, who used Eyeon Software's Digital Fusion to manage particles, paintings, and three layers of smoke. "You've got to have at least three CG smoke layers moving at different speeds to get a nice shift in perspective," says Barron. "Two are not enough. Your mind can absorb two, not three, so the complexity of three makes the scene look real."

The last shot in the sequence is a so-called "God's-eye view" of the battle. To plan the shot, Cotter built a 3D model of the Alamo from architectural plans and used it to position the camera. Then he put a CG camera on a terrain map that matched the location where the film would be shot, to visualize the view with different lenses and from various heights. "When we were on location, we knew exactly where to put the crane, how high it would be, and what lens to use," says Cotter. "I took a snapshot when we were all set up, and it looked exactly like the previz."
To heighten emotion outside the Alamo while Davy Crockett plays his fiddle inside, Digital Matte World artists enhanced the original shot (top) by adding troops in the city beyond and a more dramatic sunset (bottom).




With the camera on the crane locked off, the Matte World Digital crew took five shots with the extras charging the Alamo in various places and one of the extras fighting inside. The shots would later be spliced together into a composite image. "The elements had to be historically accurate," says Rivera. "If there were too many troops on the southeast wall, we had to remove some. Fortunately, the elements were shot correctly, so we barely did any roto." During the battle, flares illuminate the battlefield. The flares and the fires were shot against an unlit background and added to the plate; lighting was adjusted beneath as the flares soared over the Alamo.

Because the cast on location used black powder, there was smoke in the plate—sometimes too much or not enough—so Rivera had to remove dense smoke in some areas, but add it to others. Also, he added gunfire, working in Adobe's After Effects to animate the individual elements. When finished, the crew had created an animated painting of a battle that looked completely realistic.

In one shot, looking out from the Alamo toward San Antonio, where the Mexican troops were beginning to encircle the fort, the camera begins with a close-up of Lieutenant Colonel Travis in the fort and then circles around the fort to end up back at the beginning. For this, Matte World Digital created a cyclorama from moving footage. "The technique was similar to the one we used for the parade scene, but far more complex," says Cotter.

First, the crew created a previsualization to predict camera angles. As they shot sections of the real scene, they began stitching the shots together until they had mapped a reproduction of the scene inside a sphere. The motion of the original steadicam footage was used to drive the virtual world, so the shot could move from the real (the close-up at the start), to the virtual, and then back to the real at the beginning. Smith added troops to the virtual world, altered some of the buildings, and managed the compositing for the shot.
The Alamo set, built on a ranch outside Austin (top), was transformed into a fiery battle by Matte World Digital artists, who spliced together slices of action photographed with a locked-off camera and composited the images into the final scene (bo




Putting the complete world for the 360-degree shot into the computer took a terabyte of data, but it was worth it.

"Our virtual-camera technique gave the director a way to achieve the shot he wanted without dealing with the almost impossible logistics and expense of having thousands of real troops standing around in 90-degree heat all day," says Barron. "When we pan from the real world and enter our virtual world, we have complete control. We can add as many troops as we want and even change the background hills that are covered with those troops to bring them closer to the camera for dramatic effect."

For some films, visual effects allow directors to create fantasy worlds. For this film, that control allowed the filmmakers to tell a legend in a way that hadn't been done before.

Barbara Robertson is a contributing editor for Computer Graphics World and a freelance journalist specializing in computer graphics, visual effects, and animation. She can be reached at BarbaraRR@comcast.net.


Adobe www.adobe.com
Alias www.alias.com
Discreet www.discreet.com
Eyeon Software www.eyeonline.com
Pinnacle Systems www.pinnaclesys.com
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