Times Square was one of the two locations entirely rebuilt in the computer. In hindsight, Janek Sirrs, the overall vfx supervisor, thinks they may not have gone far enough with the look of abandoned New York. 

Designing Mutated Humans
Paralleling the huge environment assignment, the team also tackled a massive character animation challenge. "We not only had to start from scratch in the middle of production, but we also needed to build creatures that could hold up very close to camera while delivering a real emotional performance," Smith says. "It meant we had to do our look development and work on the shots at the same time. Luckily, we were able to hold off the most intense shots until the very end of production."

Although the prosthetics approach had been cancelled, the team decided to have live performers playing the Infected on set in most occasions -- a technique that had proved very successful on Lord of the Rings or I, Robot. Wearing gray suit, the performers allowed cameramen, the director, and Will Smith to visualize the action and to create the right feel for any given scene. The consequence was that every performer had to be painstakingly removed from frame in postproduction. Executed by Imageworks India, the task turned out to be quite a challenge as, in many cases, there was no clean plate available, a consequence of Lawrence's hand-held, dynamic shooting style.

"Originally, we were hoping to be able to cover the performers with the CG characters, but it just didn't work," Smith says. "Two facts played against it. First, the creatures are extremely thin, with a lot of negative areas, which meant that they would never have covered up the performers' body. Second, Francis opted for a fairly different performance than what had been captured on set. So, many of the Infected actions were more energetic than the original footage."

Modeling work began with a full body scan of the performers, which provided with a good starting point for proportions. The Infected were built based on maquettes designed by Patrick Tatopoulos Studios. Using Maya, the team first modeled two main "Alpha" characters -- a male and a female -- that formed the basis for all other creatures. From these models, two additional male and female body types were created. By altering these six key body types in height, thinness, depth and width, modelers were then able to build 43 different models.

"Textures required a lot of care, as the Infected have a slightly translucent skin," Smith explains. "Since those creatures don't have any body fat, it meant we had to show the next layer, which was muscles and tendons. To this purpose, we looked at many anatomy books for reference -- something Imageworks had already done for Hollow Man. It gave us the right structure for the muscles layer. We also went to the grocery store and bought all kind of meat. We then put it up on our rooftop and let it sit out in the sun for many days, while we took daily photographs to capture the progression. In the end, we had to hold our breath to shoot it... It gave us different ideas of how diseased flesh might look."

After this initial study, the creatures were built in three layers: bone structure, muscle layer and translucent skin. The muscle layer also had a certain degree of translucency to allow for light penetrating qualities. The bone layer underneath prevented light from making the body glow too much. Obviously, these three layers are part of every CG animation model at Imageworks. They are used to drive the animation and the deformations of the outer surface of a character. In this case though, the layers were also built to render, which meant they had to have their own textured surface.