To test this, a small model of the Colosseum was placed on one of Shepperton Studios’ soundstages to show how shadows would play on the stands using a light to represent the sun. It was evident to all that a practical velarium was necessary. "The practical velarium served many different purposes," Nelson says. "It would make all the shots where we were staying on set have the dramatic lighting that Ridley wanted, and it would make all the stuff where we were extending the set up into the second and third tiers that much better, because we would have real shadow cues to work from off the real crowd and foreground in order to match the digital crowd in the background. It was money well-spent."
For the interior composition, the visual-effects crew shot as many real references as possible before turning to the computer. "The programs we used to model the Colosseum were Softimage and Alias/Wavefront," specifies Nelson. "It was choreographed in Softimage and rendered in Renderman with open shade information achieved using radiosity techniques in Lightscape. It was composited on Flames and Infernos. All the Colosseum work was accomplished at Mill Film in London and supervised by Tim Burke, Rob Harvey and Laurent Huguenolt."
Another notably eye-popping shot is the 360-degree shot revolving around Maximus in the center of the Colosseum that reveals the entire arena and capacity crowd. "That particular shot began in prepro," Nelson explains. "We built the Colosseum off blueprints from [production designer] Arthur Max , which clearly defined what was going to be built as a real set and what was going to be extended as CG. We modeled the Colosseum in Softimage and Alias, then we shot real textures of the Colosseum after the practical set was built. We used those textures to map onto our CG set extension.
"For the crowd," he continues, "Laurent Huguenolt had worked out a method where we could take a six-foot-high virtual card and map a real person onto that in each seat, meaning we were putting real people in each seat of the Colosseum, and since the Colosseum had three-dimensional integrity and was three-dimensionally intact in the computer, the people would appear correct from any angle on the floor."
Realizing that it is difficult to turn hard light into soft light, we devised a method to give the effects artists control over the masses. Nelson elaborates, "The best way to [light] is to bake in a good key-to-fill ratio into our plate. We worked out an idea Rob Harvey came up with called the ’photobooth method’ by shooting people on a greenscreen wearing togas that were made of bluescreen material. We could key the people against the green and then isolate the togas in the blue and match them to any color in the wardrobe.
"We also realized that the mappings of the individual crowd people were going to be so small that 640 x 480 video resolution, if we shot it full screen, would be more than enough resolution, because individual people were going to be less than one field high on a 2048 x 1556 image. In the photobooth, we shot using three video cameras. We shot multiple lighting setups so we could bake in hard light, soft light and backlight. About 200 people doing different actions [were photographed] in frontlight, sidelight, toplight and in open shade with the three cameras positioned as one on top, one three-quarters to the side and one from the front.
"Because we controlled each card in each seat," he continues, "we could randomize the extras’ performances, or we could make crowd reactions start in one part of the arena and move through the rest of the crowd."
The actual 360-degree move was accomplished on set using a Steadicam by Klemens Becker. "We match-moved all the moves in just by having markers when we shot the Steadicam that were accurately surveyed by Chris Shaw, our match-mover on set. He had a stereo camera; we worked with photogrammetry methods with stereo Nikon images to survey the set. The 360 match-moving was a beast. Rendering and motion blur was done using Renderman with shade information coming from Lightscape, although some of the motion blur was put in using 2-D in post. Renderman is the best filtering of all the photo-realistic renderers."
Even the ferocious tigers were not spared the effects tinkering. "When working with wild animals," Nelson relates, "no matter how well-trained they are, they do what they want to do. They take direction up to a point, but they wouldn’t give us the really high-jeopardy stuff that we needed in the proximity of the actors. With tigers, you just put on a 1000-foot mag and let it roll, because you never know when the animal is going to do what you want. We got what we could get, then we went back and just shot the fight with either the tiger there or not."
The effects team worked with editor Pietro Scalia, who would take the video taps for the day, dump them into an Avid and cut together the fight sequences. The following day, he would present them with a list of what was still needed, such as a tiger swiping at Maximus in a certain shot.
"We knew exactly what we were going for," Nelson says, "and we didn’t even need to wait for the film to go to London to get souped and come back. We went back in roughly at the same time of day with the same lens for locked-off plates of tigers against bluescreen. After determining which tiger performances worked the best, it became a direct bluescreen pull with a lot of roto work in the plate with Maximus in it. If there was a tiger already in the shot, we would have to take it out with a clean plate and then put in a new tiger, sometimes behind some people and in front of others, and then add the dust in the arena. If it was a moving shot, we would set up the plate that we needed but shoot it locked off. We would track the locked-off plate back into the moving shot."
Even though Nelson has seen the finished film numerous times, he is still amazed at how visual effects enlarged the scope of Gladiator. "There are a lot of shots I look at now and don’t even realize there was no set there!" he muses. "We had one shot called the ’Wembley Stadium shot.’ During the second half of every English soccer match, there is always a shot from the last row of the stadium looking down, so we had one of those during one of the battles. I look at the original plate, and I see ocean in the background, but in the finished plate there are three tiers of screaming fans!
"What makes me the proudest about this picture is," he continues, "after the first assembly, when we had a bunch of really rough effects in it, Ridley came up to me and said, ’John, the thing that I am very pleased with is it doesn’t really seem like a visual effects movie.’ That was a very high compliment."