Maybe it was those eye-popping fish in her last project, Finding Nemo, or that trip to Paris in the autumn light. But there she was, pitching a risky idea for the visual style of a new work, what would become the animated film Ratatouille.

“I had an idea for this look that I’d wanted to do for a long time, since A Bug’s Life. Different than we’d done before at Pixar,” said Sharon Calahan, the director of photography and lighting who led the film’s illumination and colour team. “I wanted a dipped-in-chocolate look.” So far, so good. “I wanted the audience to struggle a bit to see what was going on.”

She wanted to take the story of a rat who dreams of becoming a chef in Paris to the dark side.

Prior to telling Pixar Animation Studios she wanted to paint their rat tale black, so to speak, Calahan had—besides the bug and fish flicks—directed lighting and photography on both Toy Story films. On a recent morning, she set up an easel to paint on a bluff in Bodega Bay, California, as she began a summer break from Pixar.

“This is the first chunk of time I’ve ever taken off,” Calahan said, cliffside on her cellphone. She knows Pixar will soon send smoke signals about the next project. But for now, “It’s a mystery, which is good because I don’t have to think about it, because I can’t not think about it.”

For months, she couldn’t not think about Ratatouille. And on Wednesday (June 25) at the Vancity Theatre, she’ll give a tour of the Oscar-winning film at a sold-out event presented by ACM SIGGRAPH, called Teasing the Senses: The Visual Style of Ratatouille.

Calahan, who attended art school before it was even possible to study computer animation and calls herself “a fossil in this business”, compared her role as Ratatouille’s lighting director with those of her counterparts working on live-action films. “The thought processes are the same, getting composition and light onto the screen. Obviously the tools are different,” Calahan said.

Her tools involve PCs, Macs, and Pixar’s own lighting and rendering software—plus the 3-D graphics and modelling program Maya and Photoshop. “I’m responsible for the final look of the film,” Calahan said. “I direct the lighting, with a team of 40 people. I’m involved with deciding how surfaces react to light, what colours look like, how they translate into final images. We’re the end of the pipeline.”

With Ratatouille, it was a cobblestone-and-computer path to pipeline’s end. First, Paris. “Harley [Jessup, the production designer] and I spent a week running around Paris like crazed tourists, taking photos,” Calahan recalled. “We wanted the movie set in fall, so we went in October to see what the light looked like.” She’d forgotten how charming the city’s limestone buildings are. “The light gets really warm bouncing between those buildings. Reds popped.” They decided to save red as a special colour.

Could they successfully capture Paris? “That was one of our biggest worries,” Calahan said. “We’re a bunch of dumb Americans trying to make a film about Paris. We wanted to romanticize, make it feel like your best memory of it.” And if one is a rat? “We were right down on those cobblestones.”

But back to black. “I wanted to turn the way the computer thinks on its head,” Calahan said. A computer thinks that when you remove illumination it must make everything “muddy, grey, cool”. Calahan imagined “a rich, filmic, warm-shadows look”.

There was, however, a director (Brad Bird) and some animators to consider. “Once the animators put work into every detail, you generally want to see it. They’re disappointed if it’s, you know, black,” she said, laughing. “I was holding back and Brad said, ‘No, no, you can go darker.’ I went really dark, and he’s like, ‘Okay, maybe put a bit back in.’ ”

“When Remy is running around in the walls, I wanted to see how little light we could get away with,” Calahan said. “I wanted audiences’ eyes to dilate in the darkness so when Remy gets up on the roof and realizes he’s in Paris, there’s a dazzling payoff.” That rooftop scene overlooking Paris and the Eiffel Tower would become an iconic moment in the film.

Calahan had her city of lights and dark, ratty places. They created Gusteau’s tricky, satiny-surfaced kitchen. They worried about food. “Food is the movie’s heart. Everybody panicked about how to make it look good,” she said. There could be no creepiness. “Food is like CG [computer-generated] humans. If it looks too hyper-real, it gets creepy-looking.” They followed chef Thomas Keller around the French Laundry restaurant kitchen; one day, he invented the swirling ratatouille Remy would create in the film. They photographed food until it became “inedible”.

Back in Bodega Bay, Calahan remembered she hadn’t had lunch. She’s happy with the visually tasty Ratatouille, but there’s a new film coming out that she consulted on: “Wait until you see WALL-E. It’s absolutely stunning.” But first, some ratatouille.