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Issue: Volume: 30 Issue: 7 (July 2007)

Most Delicious


 The most unlikely ingredients often create the most delectable dishes, the unexpected flavors transforming food into a mind-altering, tongue-tingling sensation.Listen to food critic Hal Rubenstein waxing rhapsodic in New York Magazine: “…the unexpected ingredients…expand the boundaries of a cuisine and of our desires…. The briny sharpness of braised artichokes with mizuna leaves squares off against soothing goat cheese and roasted peppers, resolving into a delicious truce. Delicately folded goat-cheese tortelloni almost floating above the fork are enveloped in a wondrous coating of dried orange and rarely used wild-fennel pollen.”

Remarkably, Pixar has stirred that feeling into a CG animation with Walt Disney Pictures’ Ratatouille, the studio’s eighth feature film. But, creating food that teases a mouth-watering response was only one challenge for this film.

Ratatouille tells the unexpected yet deliciously hilarious story of a rat named Remy who has a highly developed sense of smell, a talent for combining flavors, and an appreciation of fine cuisine. When Remy slips into the kitchen of Gusteau’s famous restaurant in Paris, he secretly concocts gourmet dishes that astonish the chefs, patrons, and food critics—all of whom would be horrified if they knew. Mon Dieu!

How could this work, you might ask. A rat cooking in a Parisian restaurant? CG food that looks realistic enough to tickle your taste buds? 

Step into Pixar’s kitchen and meet the chefs who cooked up Ratatouille’s magical recipe.

“There’s a certain power that comes from aversion,” says director Brad Bird of the rat in the kitchen.

“We had to bend the canons of CG,” says Sharon Calahan, director of photography/lighting, who analyzed food photography to develop the film’s look. “I wanted everything to look juicy and succulent in its own way.”
 
Remy, the little bluish-gray rat shown at left and above, peeking out
from Linguini’s shirt, concocts gourmet dishes in a Parisian restaurant with Linguini’s help.
 
Stirring the Pot
 
The story almost didn’t work. A year and a half before the film’s release date, Pixar’s executive producer John Lasseter, president Ed Catmull, and then CEO Steve Jobs asked Bird, who had won an Oscar for The Incredibles and Annies for that film and The Iron Giant, to step into the production.

“Everyone believed in the idea, but it hadn’t coalesced into a story,” Bird says. “I kept the premise and kept the characters, but I wrote a new script. I used only two shots from the previous version and two lines of dialog.” (One line is, “You are fired. F-I-R-E-D,” which Skinner, a chef in charge of Gusteau’s kitchen, shouts to Alfredo Linguini, a garbage boy.)

Even though Bird kept the characters, he made major changes to some. First, he turned the rats into rats. Until Bird became director, to soften the impact of seeing a disgusting rodent in a kitchen, all the rats had been cute and cartoony. “I felt that was a big mistake,” says Bird. “Putting a rat that wants to be a great chef in a kitchen is the height of absurdity. Remy aspires to be human, but in the early version, the rats were like tiny humans. The rats weren’t ratty.”

By making Remy and his family act like rats, when Remy chose to walk upright, that action emphasized a story point. An expensive story point. To put the rats on all fours, Pixar had to rebuild the entire rat cast using a different mesh and articulation. “The bipedal articulation didn’t work when the rats were on all fours,” says Mark Walsh, one of two supervising animators. “So after about a year of work, everything changed.” 

Dylan Brown, the other supervising animator, adds, “A rat moves its shoulders from the inside out, but humans move from the outside in.” Moreover, even though Remy chooses to be bipedal when he’s interested in cooking, at other times, he continues to scamper on all fours. And like real rats, he and his family can squeeze through tiny holes, so the rigs needed to incorporate squash and stretch.

“It’s easy to build a quadruped, and it’s easy to build a biped, but we had to interpolate rigs,” says Brian Green, character supervisor. “It gave us much angst. Within a shot, Remy could walk on all fours and then stand up, grab a spoon, and start cooking.”

Bird also gave Collette, the only female chef, a larger role, and he killed the owner of the restaurant, the five-star chef, Gusteau. “Brad [Bird] came to us one day and said, ‘Gusteau is dead,’” Walsh recalls. “Everyone’s face went pale. Gusteau had been articulated and modeled. Then Brad said, ‘But, he’s Remy’s conscience, his inspiration. He’ll show up in the movie as this sprite guy.’ People looked at Brad with their heads titled to one side and their eyes half-lidded.” Gusteau became the unexpected ingredient.

 In Ratatouille, Remy never talks to the human chefs in the kitchen. He’s a rat; he talks only to his family. And, to Gusteau. Gusteau appears as a ghost, having committed suicide after food critic Anton Ego gave him only four stars, not five. It’s his cookbook, “Anyone Can Cook,” that inspires Remy—and also saves his life.
 
A splash of fluid simulation (at top) and a dollop of soft-body simulation
(at bottom) helped the little CG chef stir soups, flip omelets, and cook other tasty dishes.

Le Milieu

The film opens in the French countryside, with a voice-over of Remy telling his tale. It’s clear from the opening scene, a rustic cottage framed in autumn leaves, that Pixar has created something unique. The light. The colors. The textures. Ratatouille is not a film with brightly colored toys, fish, bugs, or cars.

“We tried to make this film look different,” says Michael Fong, supervising technical director. “One of the big things was to break away from what standard CG looks like. We got rid of straight lines and did a lot of hand tweaking. We wanted it to feel handmade. The other part is lighting and shading.”

In the countryside, Remy introduces good taste to his brother Emile, who is happy eating garbage. Their father puts Remy’s nose to work, though, sniffing for poison before allowing the pack to eat the garbage they collected.

To animate the rat pack, which sometimes totaled a thousand rats, Pixar used Massive software for the first time. Animators created motion cycles, and a crowd team fed the cycles into Massive brains that moved bodies created with mix-and-match parts. In addition, Pixar developed tools to pull an individual rat out of the crowd simulation and move it into the studio’s proprietary animation software, Menv. Pixar also uses Autodesk’s Maya for modeling and its in-house software, Geppetto, for rigging.

When Remy explores Granny’s cottage, the house from the opening scene, he discovers Gusteau’s cookbook. But, Granny spots Remy and his family and opens fire with her shotgun. The rats run to their boats. The water sweeps them into a storm drain, and Remy rides out a raging flood by hanging onto the cookbook.

To create the flood, the technical directors used the same simulator that had created water for Finding Nemo, but changed the mesh surfaces—that is, changed the way they built meshes from the simulation data.

“Think of a big vat of Ping-Pong balls,” Fong explains. “The simulator moves them in certain ways like big waves. We find the surface and make a mesh out of it. In Nemo, when we did that, the 3D mesh was temporally coherent, but we lost some of the detail. With Ratatouille, when we threw the sheet over the Ping-Pong balls, we got more detail. We saw the resolution at a Ping-Pong level.” For Nemo, Pixar had used particle-level sets; for Ratatouille, they switched to more of an implicit solution using research from Chen Shen and others at the University of California at Berkeley.

Alone now, Remy pulls himself out of the water and onto a ledge under a storm grate. There, he rests and pages through the cookbook. When he reaches Gusteau’s page, the image of the great chef becomes animated. Gusteau rises from the page, and the now floating, semi-transparent spirit tells Remy to go up and look around. When Remy does, he discovers he’s in Paris, and it’s beautiful.
 
Innovative illumination models gave lighting artists a new palette to
capture the soft light of Paris and still saturate the environment with rich color.

L’ambiance

The early story idea for this film came from Jan Pinkava, who won an Oscar for his short film “Geri’s Game,” and he created the early designs for Ratatouille’s world, as well.

“I hope it feels like it did for us when we were running around Paris in the fall,” says Calahan, “the softness of light, the trees turning color. There are a lot of neutral tones in the film, even on the streets of Paris with its limestone buildings and granite streets. I wanted to use color sparingly, to use a more limited palette, but at the same time, to get more color into our darks. And where we wanted color, I wanted it lush and rich.” To create this look, Calahan worked with effects supervisor Apurva Shah to develop a new illumination model. “The key aspect was that we separated saturation from luminance [contrast],” says Shah.

Shah explains that many people in computer graphics believe that the math of CG imagery should follow physics. But, even sophisticated CG illumination models only approximate how light bounces in a scene to calculate color. “You can’t get all the subtle softness,” Shah says.

Moreover, adding rich color to dark areas often increases contrast. “Typically, the renderer does its physics to calculate color, and then you apply a look-up curve; you use tonal mapping,” says Shah. “But, that influences contrast in the image. That’s why it is nice to separate contrast and saturation. If the only way to increase saturation in the darks is by pushing contrast, you get into a place that doesn’t look real.”

With that separation introduced into the illumination model at a basic level, Calahan and the lighting leads created the balance they wanted and established key values. “We got rid of the icky grays,” Calahan says. “We could saturate colors in the darks and de-saturate color in the lights. It’s definitely a different way of thinking about lighting. CG purists think it’s the wrong way. And some people would argue that the right place to do this is in compositing, where they have more control. But I wanted things to be done in-camera.”

In addition to separating contrast and saturation in the illumination model, Shah and Calahan decided to work in non-linear color space. “From a tonal standpoint, people doing CG tend to use linear color space,” Shah explains. “We find in linear space that light falls off too hard or adds up in a slightly weird way, so we have a different space, a non-linear space. Broadly speaking, it’s more like how things happen in nature. Many people do this on a light-by-light basis, but with Ratatouille, we introduced that fundamentally into our illumination model. It automatically works with every prop in every sequence.” For example, Calahan explains, in the color space used before, when an artist added two lights together, it increased the brightness noticeably, but didn’t double it. The light added up. In the new color space, however, two lights made something doubly bright.

“None of our tools worked the same way,” Calahan says. “Low-intensity lights that you think wouldn’t contribute much could affect the look of a scene. But we quickly adapted. To me, it felt more natural. It’s like when you change an f-stop, you expect it to halve or double the light.”

In addition, Pixar introduced depth-based tinting in the shaders. “If you look at a splash of wine on the side of the glass, it’s almost transparent,” says Shah. “The color builds.”
 
Character designers created 20 cutting-edge primary characters, each
with a distinct silhouette and personality, and approximately 50 secondary characters.

Gourmet Kitchen

When Remy climbs from the storm drain onto the streets of Paris, he’s across the street from Gusteau’s restaurant. Atop the building, a giant rendition of Gusteau in neon becomes animated and encourages Remy to visit the kitchen. 

At first, Remy only peeks inside the glorious, bustling kitchen filled with gleaming copper pots and pans—frying pans, crepe pans, saucepans, stockpots, fish poachers, a wok, casseroles, roasting pans. Chefs wearing stiff white coats and tall white hats chop vegetables, stir soups, knead bread dough, and sauté fish. A waiter rushes in from the dining room.

Much of the action in the rest of the film takes place in the kitchen; it had to feel believable. “The grout lines aren’t straight in the tiles,” says Fong. “The reflections are blurry.”

Yet, creating the soft reflections in the kitchen’s multiple burnished and dented surfaces, the stainless steel table, and the copper pots and pans became compute-intensive. “The problem with raytraced reflections is that uneven surfaces bounce the rays a lot,” says Shah. “And, when you want a soft reflection, you set the cone angle big, so you need lots of rays.”

Using a reflection map would have been faster, but it wouldn’t have produced correct distortions. “So, we took the radiance of the world and baked that illumination into a [RenderMan] brick map,” says Shah. Then, they bounced rays into that brick map. When the rays found an intersection in the baked-out map, rather than using a shade calculated at that point, they averaged the results from the collection of rays sent into the large area. “The result is that we could send out fewer rays and still have the correct distortion,” he adds. And that produced kitchen surfaces with a tactile patina. 

For the wine, however, the artists used shaped reflections to give the liquid a proper sheen. And, to put textures on such liquids as soups and sauces, they developed new shaders.

Les Ingrédients

The combination of the new illumination model, new shaders, and such lighting techniques as subsurface scattering made the food look appetizing. But the food also needed to act like food, to move like food.

“The challenge for CG food is to not have it look like a play-set of plastic food,” says Walsh. “We wanted the audience to see it and say, ‘I’d like a bite of that.’ The most banal things we take for granted—chopping carrots, slicing onions, sautéing, and flambéing—were huge projects for our effects team.”

Shah’s effects team filled the kitchen with simulations. Fluid simulations for liquids and fire, soft-body simulations for food on plates and vegetables in crates, gas simulations for steam, and rigid-body simulations for slicing and dicing.

For fluids, Pixar used the simulation engine developed for the water in Finding Nemo, Maya fluid simulations, and an open-source dynamics engine developed at Stanford. In addition, a new simulator handled thick sauces. “Brad Bird was really picky with small bodies of water,” says Fong. “Soups and sauces have a different viscosity than water.” 

Soft-body simulation helped dress the sets—and the plates. “In CG, it’s easy to make things seem stacked up and linear, barely touching, like they’re sitting on eggshells,” says Fong. “We wanted to make sure the objects felt kind of squishy.”

For bread, they used an extension of soft-body dynamics. “Brad [Bird’s] brief was to think of the dough as a little version of Pompidou,” says Shah, referring to the plump chef who kneads the dough. “We did a lot of work on the internal structure of bread so that while it collides and gives with pressure, it also maintains volume.” To help shape the bread, they could drive the internal springs with target shapes.

When someone slices the bread, you see a cellular structure inside. “We couldn’t just do displacement,” says Fong. “We mathematically calculate bubble density and procedurally form the bubbles, then slice through that volumetrically.”

For the vegetables, the effects team developed a chopping system that utilizes rigid-body simulation. First, animators performed the motion—Colette chopping celery, for example. Then, the team analyzed the cutting plane (the direction the knife took through the celery), broke apart the geometry appropriately, and ran a rigid-body simulation on the resulting pieces. “We didn’t prejudice the animation,” says Shah. “We looked at how forceful the knife is and whether the cut is done with confidence or is clumsy.” That animation told the effects team how to set the forces in the rigid-body simulator, which then caused the vegetables to, perhaps, jump on the cutting board, roll off, or move slightly.

Quelle Horreur! 

When Remy looks into the kitchen, he sees garbage boy Alfredo Linguini toss some ingredients into the soup, as if he could cook. Appalled by Linguini’s choices, Remy sneaks into the kitchen and fixes the soup. When Skinner, the head chef, realizes that Linguini touched the soup, he fires him. “You’re F-I-R-E-D.” He doesn’t yet know about Remy’s contribution.

To simulate the chefs’ stiff clothes, Pixar used its own cloth simulator, based on a spring mesh model. “We had to make it more robust, though,” says Green. “When the animators did moves that were too crazy, we invented a new technology so we could pin cloth to a pose and construct to a pose.” To move Skinner’s clothes during a wild pirouette, the effects artists turned animation poses into a series of simulation targets. “We can bind the simulation to the target shapes, say to the top of an apron, and then let the bottom swing around more,” Green says.

Pixar also developed new hair-simulation techniques. “Colette has fairly long hair that we simulated for every shot,” says Green. “To maintain the thick volume, we did hair-to-hair collision. Without it, all the hair interpenetrated.”

Because the rats have short, stiff hair, simulating one rat’s fur was relatively easy by comparison. But, Remy’s pack created some interesting render times. “The crowds got pretty hairy,” says Green. “Each rat had 500,000 hairs, so that could be as many as 500 million hairs in a shot.”

Knowing that they might have as many as 900 to 1000 rats in a shot, Pixar formed a RenderSpeed team, and one problem that team tackled was rendering hair. “We knew that in Monsters, Inc., one shot of Sullivan took between six or seven hours to render,” says Fong. “The machines were slower then, but that was still a long time.”

Thus, the technical directors had the rat hair automatically grow wider and thicker as the rats moved away from the camera. “Because we made the fur bigger, we could reduce the amount,” Fong says. “We did test renders, and you couldn’t tell the difference.”

Cooking School

After Skinner fires Linguini, two important plot points take place: The patrons love the soup everyone thinks Linguini created, and Skinner spots Remy in the kitchen. Everyone freaks out. A rat in the kitchen! Ordered to kill the rat, Linguini traps Remy in a glass jar. But, Linguini knows that Remy cooked the soup, and Linguini needs a job. They agree to partner. Two problems: Remy doesn’t talk, and he can’t be seen in the kitchen.

When Bird joined the project, animators were already working with the notion that Remy would puppeteer Linguini, essentially drive his arms and body, by sitting on top of his head and pulling his hair as though clumps of hair were joysticks.

“It only kind of worked,” says Bird. “The idea wasn’t bulletproof.” Bird made two changes to sell the idea. Rather than have Remy peek out from under Linguini’s tall chef hat, which took time and could happen only when no other chefs were looking, Bird made the hat transparent from the inside out. From inside the hat, Remy could see out into the bright room, but unless a light shone through the hat just right, no one could see Remy inside.

Bird also added a wild practice session in Linguini’s apartment. Remy blindfolded the gangly Linguini and had him cook a meal by driving him with the hair-clump joysticks. After one hilarious mishap after another, Remy learns how to control this implausible system. By the time the blindfolded Linguini pours a glass of wine without spilling a drop, we’re convinced.

At Pixar, Dylan Brown demonstrates how the animators drove Remy. On Brown’s screen, a flat-shaded Remy grasps a blocky clump of Linguini’s hair in each little rat fist. Running down the right side on Brown’s screen is a list of approximately 20 “avars” (animation variables). In another window, a long vertical curve lies underneath a frame count. “This is our palette of controls,” Brown says. He picks an avar labeled “Head FB,” and Remy nods his head, forward and backward.

Then, Brown animates Remy by clicking handles on the curve to change its shape in each frame, that is, over time. The smooth vertical curve becomes a rippled line. Walsh continues the explanation: “We use curves to slow in, slow out, and overshoot to control the movement between keyframes.”

Brown adds, “It’s about the transference of energy. Also, it informs motion blur, which is calculated on sub-frames.”
 

The roughly animated Linguini and Colette (at top, left) receive hair
and clothes (at top, middle) that effects artists simulated using a
number of new techniques. Texture artists add detail (at top, right),
 and lighting artists add warmth and a patina of reality
 in the final image (bottom).

Voila!

In addition to these standard controls, Pixar created new tools for the Ratatouille animators. When Brown pushes Linguini’s fist into his belly on-screen, the geometry of the fist doesn’t pass through the geometry of the belly, as is typical in 3D animation systems. Instead, Linguini’s belly sinks in and the belly’s surface geometry reforms around Linguini’s fist.

“Before, with our system, if we caricatured too much, like extended the mouth too far, things would either blow up or we would have to wait for simulation,” says Walsh. For Toy Story, Walsh explains, characters had a bladder balloon in their cheeks that stayed in the same spot. For Nemo, the cheeks followed the corner of the mouth. “We had a fake muscle system,” he says. “And for The Incredibles, we improved the muscle system. But for this film, we wanted characters to touch each other, interact with the environment, and squish against each other, and we wanted to see all that while we were animating. So, we designed the ‘collisions project.’”

Software engineer Gordon Cameron and animation character developer Robert Russ devised a system of collision objects that let animators push the geometry around in a way that looked like a volume-preservation simulation.

“These aren’t simulations, because we wanted to give animators direct control,” says Green. “The collision objects are all over the characters, and each collision object can have a different response.” A character might have collision objects in its fingers that react differently from the collision objects in its cheeks. A chest collides in a different way than a belly. When Gusteau touches his face, for example, it deforms appropriately. His eye sockets remain solid, but his cheeks squish because in the geometry, points collide and move out of the way of each other. The geometry pushes in and bulges out. 

When animators wanted characters to interact with vegetables and props, they simply attached collision primitives, spheres, triangles, and so forth, to the geometry. “If I wanted a character to sit in a chair, I’d design the chair to be a collision object so points on the chair could talk to the character,” says Walsh. “When we have objects that aren’t collision-ready—maybe a knife, a fork, or a piece of cheese—we’d attach a collision-primitive shape. It really helped the characters fit in the world and interact with it.”

And what a world. The complex ingredients in Pixar’s Ratatouille recipe have combined to expand, as did the food in the critic’s review, the boundaries of animated filmmaking: The ratty-acting rats. The unexpected, fantastical Gusteau. Cloth, hair, and crowd simulations. New lighting techniques that fill the blacks with rich colors and cast soft reflections on well-used copper pots and stainless steel counters. Fluid simulations that help digital chefs pour sauces and stir soups. Soft-body simulations to nestle tomatoes in crates. A vegetable chopping system. An environment that looks handcrafted. Characters with bodies that react to the environment. Talented animators and artists, and a genius of a director who knows how to tell a story.
 
Animators created the illusion that Remy controlled Linguini’s
actions when he pulled on clumps of the redheaded teenager’s hair.

“Of all the movies I’ve worked on, I’m most proud of this one,” says Calahan. “I think it’s the best movie we’ve done.”

Bon appétit!


Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at BarbaraRR@comcast.net.
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