Late '20s Los Angeles is a major character in Changeling. CIS Vancover created "peripheral imagery" to transport the viewer back in time. All images © Universal. Courtesy of CIS Vancouver.

Changeling, the true life crime drama from director Clint Eastwood (now playing through Universal), does not make obvious use of visual effects, but wouldn't be the same movie without them.

Changeling stars Angelina Jolie as a single mother in 1928 Los Angeles whose nine-year-old son goes missing. When the police return to her a boy they claim is her son but she says it's not, it opens up a hot house of police corruption.

And that city is a major character in the film, brought to vintage life by Overall Visual Effects Supervisor Michael Owens working with CIS Vancouver and Pac Title.

Owens says the vfx work began with research into what the city was like in 1928 -- research of historical photographs and data that revealed the city had the most dense urban core in the world at the time.

Recreating that setting required shots what Owens describes as "peripheral imagery."

"We knew what we were getting ourselves into," he says. "It was 3D set extensions and Massive CG population. Cars, trucks, trains and street furniture -- that sort of thing," Owens adds.

Principal photography took place mostly on the back lot at Universal -- a location so well used in so many films that Owens felt it was important to mask familiar structures as much as possible. The back lot was mapped out with an eye toward figuring out where visual effects would begin and end in relation to the physical buildings.

Massive was used to populate the streets with cars, trucks, trains and street furniture.

"We changed out a lot buildings that were foreground-ish, midground-ish buildings just so that you couldn't recognize that stuff," he says.

Geoffrey Hancock, visual effects supervisor for the film at CIS Vancouver, says they created the right look using a collection of architectural elements from the era that could be recombined to create a variety of buildings.

"We could rearrange them and restack them to create either wider buildings or taller buildings of that same architectural style and then rearrange their order on the block so that you could create a very different looking city with only minor texture differences," Hancock explains.

Those decisions were based on vintage aerial photographs of downtown Los Angeles and tried to reflect the real geography of the city as a way to orient the audience in the story. "Having that consistency between scenes and shots we felt was going to help the audience get located and feel like they could understand the environment," he continues.

CIS used primarily Maya to animate and mental ray to render the city scenes, Hancock offers. A number of matte paintings were created using XSI and Maya, and some 2D work was done using Digital Fusion.

The project also called for extensive city crowd scenes, for which Owens says they turned to a combination of motion capture and the Massive crowd-generating software.

"We were planning to integrate Massive to a certain extent with live-action extras," Owens suggests. It was an ambitious task that presented its fair share of problems. "And up to the point where you're not mixing them, it works pretty darn well, because the Massive brain tells everybody where to go. But as soon as they started mixing around with the live action characters, then you have to encourage them to go one direction so you don't have to remove a live-action extra."

Actors were recorded with motion capture to get motions that matched the era. Owens says people tended to wear much more formal clothes, such as high heels for women and wool suits for men even in summer, and also moved in a more formal fashion.

The quintessential shot of this type is the final shot, which looks down a busy downtown street with City Hall in the distance while the head credits roll. Owens says he was the one who suggested the shot to Eastwood as a way to close the movie.