<em>Ratatouille</em> Pixar Style: <em>Bon Appétit</em>

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With Ratatouille [1], Brad Bird and Pixar have set a new standard once again for 3D animation and storytelling. They offer the most beautiful eye candy yet in CGI. All images © Disney Enterprises Inc. and Pixar Animation Studios.

With Ratatouille (opening June 29, 2007), Brad Bird and Pixar have set a new standard once again for 3D animation and storytelling. The premise about a French rat that aspires to be a chef is deliciously absurd and imaginative, with enough twists and turns for -- you guessed it: a French farce. The attention to detail is remarkable (check out their little beating hearts whenever they get excited). What's more, Ratatouille offers the most beautiful eye candy yet in CGI, between the romantic depiction of Paris, the mouth-watering cuisine and the expressive rodents. It's about as original and sublime as you can get these days, and the most wonderful thing is that you often forget you're watching animation during this loving tribute to cooking, art and innocence.

"One of the wonderful things about this premise," Bird observes, "is that rats are death to a restaurant and a restaurant is death to rats -- and so this ups the ante on both sides and is ripe for animation that thrives on the mother's milk of caricature."

Remy (voiced by Patton Oswalt), of course, is no ordinary rat. Rather than settling for his trash-heap existence with the rest of his colony, he has cultivated a sophisticated sense of taste and smell and dreams of cooking haute cuisine. Remy gets his wish when his life is turned upside down and he's paired with a hapless garbage boy named Linguini (voiced by production designer Lou Romano) at Paris' most famous restaurant through a series of improbable deceptions.

"Originally, when I got here, [the rats] looked more like humans and their arms were toward their sides. At some expense, I had them go in and make the rats move on all fours and have their muscles work correctly." Thus, a whole year's worth of modeling was scrapped to make the rodents more rat-like but still appealing.

"There's a huge amount of engineering that goes into building these characters so the animators can use them," Bird continues. "We observed a couple of real rats for a year. One of the things we wanted to do that was real important is that when Remy gets on two legs, it's a choice to emulate humans. He has reasons for doing that. It makes it a story point and visually separates him from the other rats. If you understand the real behavior of rats, you can deviate from it with knowledge."

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A lot of engineering and research [2] went into building the characters. Here's concept art that was used.

With only nine months to animate, since Bird was plucked from the Pixar story brain trust to replace Jan Pinkava, supervising animator Mark Walsh says they took advantage of the shoot-from-the-hip predicament. As a result, there was more spontaneous energy on Ratatouille than on any previous Pixar feature. "From what I observed, the first creative instinct is what ended up on screen," Walsh confirms. "And Brad will be the first to admit that he couldn't afford to be a perfectionist on everything. So he leaned on the animators to bring their perfection to the table. He was writing the story while directing it, so it really empowered the crew. I think it was different for Brad and it was different for us. "

In fact, according to Walsh, there were even tweaks made to a few scenes after they were animated, including the courtyard exchange between Linguini and feisty chef Colette (voiced by Janeane Garofalo), and the disturbing encounter between Remy and his father outside the exterminator's office. A couple of animators sent Bird an email questioning his choices, and, later, in front of the group, Bird announced that they were redoing a scene, thanks to a great note.

"With Brad, it's all about the idea," Walsh continues, "and he's really great at explaining the significance of whatever you're doing to the overall story no matter how small it is. This was definitely the most difficult animation to date. You have so many extremities: whiskers and ears and tails. This was the first film where we relied on master rigs that we applied to other characters. It used to be that we would do each character separately, for the most part. But, when you have a whole colony of rats, we were able to drag and drop a skeletal rig and then clean it up quickly.

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Pixar found that the requirements for fur were far different than anticipated. The animators discovered it was advantageous to use less fur, but make each strand thicker on the background rats. [3]

"Also, we had this new project called 'Collisions.' We really wanted the characters to interact with their environments and with each other. If they shook each other's hand, they would actually squish. Or if they were leaning against a wall, their body would squish. Or if they hugged, they would collide with each other. There were methods to do that in the past using simulation, but we wanted to see it in the camera while we were animating so we could control the shapes. So we created software that cheats the collision, where you push into the mesh and it inflates a [bulge] around whatever shape you're trying to push into and that slides around with the character. This way the size and shape of the bulge doesn't have to be a surprise after the animation is done. That helps subtly throughout the film. When Remy grabs a saltshaker, for example, it pushes into his body.

"We also made a few tweaks to facial rig from The Incredibles [4]: we had controls to squash-and-stretch the pupils on the eyes better. The cloth was more complex here and the team made more advancements since The Incredibles, even the way they shade, including the stitching. Someone found an old textile machine manual on how to sew fabric, and they actually ran a simulation of the same pattern from this guidebook and came up with incredible textures and seams. We were able to animate just about anything and then send it to the sim department, and they were able to put clothes on things that went beyond anything [we tried before]. Now because of the collisions, there were no cloth restrictions and animators were able to create movement more freely."

As for fur, it turns out that the requirements were far different than anticipated "When we put the fur on the rats, because everyone loves the technology of that moving fur, they had it overlapping, and suddenly you get the Godzilla factor when the rats are jumping up and down," adds Walsh. "So they kept dialing it down and dialing it down until those poor fur guys ended up turning off the fur overlap. To our surprise, we found that when it gets down to that small a scale, the fur isn't that long and didn't need to be simmed, unless there was collision going on." Also, it was advantageous to use less fur but make each strand thicker on the background rats.

In terms of increased computational power, Pixar was also able to take advantage of a new partnership with Intel. The use of Intel Xeon processors with Intel's Core micro-architecture technology in the servers and workstations provided the superior computing performance behind the scene rendering of Ratatouille, helping to create never-before-seen advances, including lifelike bubbles, innovative lighting techniques and ultra-realistic dripping water effects.

One of Intel's earliest engagements with Disney/Pixar was helping optimally compile their RenderMan software for Intel architecture. One aspect of the optimization was enabling the software to take advantage of instructions added to Intel processors to better run RenderMan's workload, resulting in a 30% in software performance improvement.

A more recent engagement involved helping the Disney/Pixar RenderMan product team to thread their software to make better use of multi-core processors, dramatically increasing the performance of the software on Intel processor technologies from 2-3 to 5X depending on the number of cores.

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The studio came up with a new brick map scheme that simplified 3D representations of the environment for each shot. It worked well for the accuracy and soft patina needed, and was helpful with all the kitchen reflections. [5]

Although Pixar was able to take advantage of PRMan 13, containing the new multi-threaded super fast renderer with built-in ray tracing, it had to create several customized tools, primarily for greater control.

To optimize rendering time, the studio came up with brick maps: simplified 3D representations of the environment of each shot. Ray tracing is done from this stand-in instead of the shot's "real" environment, using an in-house technology called "Trace Radiance."

"We knew we didn't want the super sharp, ray traced reflections that we had on Cars [6]," explains Sharon Calahan, director of photography/lighting. "We couldn't afford to make them soft enough and they looked a little too gritty. We couldn't get accurate enough reflections with our old environment map technology, so we did a brick map scheme that worked really well for both the accuracy and soft patina that we needed. This is not shiny, bright, in your face. It's richer and subtler."

This was particularly helpful in dealing with all the kitchen reflections. "The weird thing is, if you do brute force ray trace reflections, as they get softer, they get more expensive, which is obviously not acceptable, so we came up with the Trace Radiance solution to basically keep the render times more reasonable and cut some corners visually that you wouldn't notice," adds effects supervisor Apurva Shah. "For example, the use of simulation for set dressing to create a plate or a dish."

Pixar also came up with "Scatter," an improved subsurface scattering system that gives the artist control over where light energy travels once it penetrates a surface and how its color changes in the process. "Subsurface scattering worked better and faster and we had more control than on The Incredibles," Calahan adds. "We also took gummy stuff on Finding Nemo [7] for fish and tuned that up and made it more robust and provided more control for the lighters. We had a gummy pass that we used for translucency as well as the subsurface scattering."

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To get the CG food [8] to look right and appealing on screen, Pixar came up with a new illumination model that allowed them to achieve greater independent control between contrast and saturation.

As Bird suggests, it all pretty much started with the food and how to take advantage of the new subsurface scattering: "We had consultants who were gourmet cooks give an overview of not only how food looks but also how things are set up in the kitchen. It's not remotely real but gives the fantasy a footing. There was a lot of effort put into even how food looks when you're preparing it. What causes sauce to curl around when people are stirring it? A lot of this is CG math and bending ones and zeros to emulate something that's organic."

Indeed, not only was there an icky factor regarding rats but with food as well. "Everyone was freaked out about CG food when we started nearly four years ago," Calahan adds. "I knew it wasn't going to be harder than anything else -- really -- once we figured it out. I also didn't want to light the food differently from the rest of the movie. I wanted to come up with an approach that was appealing and use that on everything else too. We spent a lot of time looking at both good and bad food photography and thinking about what I liked and disliked about them and came up with a vocabulary that I could share with the production designer [Harley Jessup] and everyone else on the team. Some of it was the scheme of wanting the local color of the surfaces to come through more. If you can make a tomato or broccoli look appealing... I took basic concept of that and took it to the humans and the sets, and so when you look at even the rain sequences, you see a lot of the local colors coming through the atmosphere."

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In the movie, cooking is very tightly integrated with the animation. Pixar had consultants who were gourmet cooks give an overview of not only how food looks but also how things are set up in the kitchen. [9]

To achieve greater independent control between contrast and saturation, they came up with a new illumination model at Pixar. "One of the chronic problems for the industry is that darks get very gray and muddy in CGI," Shah asserts. "We dealt with it in the past by adding colored shadows or fill light. But it always seems to look painted on and not as organic. People are very careful in picking these local colors, but then you are hostage to what happens in the illumination model ultimately to those colors. And so we did some work you retain more of that saturation in these dark colors."

"I was trying to do the opposite of what traditional computer graphics normally wants to do with how it handles light and color that falls off," adds Calahan. "In essence, I'm saturating anytime I'm losing illumination. It was more of a fix. We're going to try and turn it into something real now." Thus, Calahan and Shah are now working on implementing the new illumination model for future use.

From an effects perspective, cooking was also a challenge for Shah. "In the movie, cooking is very tightly integrated with the animation. For example, chopping. You have this very tight feedback loop with the chef's knife essentially coming down on the cutting board and chopping something up. There's obviously nothing actually there, so what we decided to do was, rather than craft the performance with all these constraints, we wrote a chopping system that analyzes the cutting planes that the knife was generating and then cut up the model post animation based on where the knife is coming down, and then rigid body simulate that to the actual motion."

Meanwhile, having dealt with large quantities of CG water in Finding Nemo and even with rapids and a sewer and a kitchen sink in Ratatouille, they needed to create a lot of small bodies of liquid related to cooking. They range from a glass of wine to a bowl being whisked or a pot of soup. "We had to actually do a lot of work post simulation to massage the shapes," Shah says. "Basically we worked on the front end with the simulator itself. We found the right parameter set, which took a lot of testing, initially. These default parameter sets tended to want to work better for larger bodies of water. We used two different simulators for the movie. For liquids, we used the simulator originally written for Nemo but with modifications and we also used a public domain simulator, Stanford's PhysBAM. Another key was we wrote our own mesher, like a surfacer, that would generate not only a liquid surface but also a parameterization for it. One of the things we found that we needed to really sell these smaller bodies of water was to texture them. We worked in-house to come up with parameterization for these surfaces."

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An early concept art showing Remy in the kitchen. [10]

Raindrops even posed a challenge in the opening sequence establishing Remy's rural environment outside of Paris. When they looked at artwork early on, they realized that the raindrops weren't just rendered as little strokes. "They didn't have a straight edge, so we used that," Shah adds. "It's a compound image made up of little particles. When the raindrops hit the river, we wrote some extra programming to create some extra undulation in the water because it doesn't disappear from a rat's perspective -- it has fallout. So you have a little simulation there that solves that connection. It just so happened that it rained here in the area, so we went out and shot rain hitting the leaves, and it happened to be the same level of rain, which was a lucky coincidence."

Pixar also created some one-offs: for rolling dough, they came up with soft body solutions. Bread was a shading problem, so they created a volumetric texture, which is what you saw with the soft crumb inside. The outside texture was more of a classic surface treatment with paint and with the right illumination properties to give that sense of structure that was required.

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Pixar needed to create a lot of small bodies of liquid related to cooking. They used the simulator originally written for Nemo, but with modifications along with a public domain simulator, Stanford's PhysBAM. [11]

"The other thing I wanted was a warm, cozy movie," Calahan acknowledges. "We retained warm tones in the dark even if the rest of the scene is cool [such as where the rats live]. Harley and I were like mad tourists taking pictures of Paris. One of the things we noticed -- and I had forgotten because I hadn't been there in a while -- was how homogenous the city looks. All the buildings are very similar in architectural style and the materials they're made of -- they're all made of limestone, so they all have a warm, honey, tan color to everything that's so inviting. And there are certain colors that stand out against that landscape. You'd always see red awnings and red flags that would pop out, so we saved red for the chase sequence through Paris. I really wanted [the villainous] Skinner's scooter to be red for that very reason. And we really wanted it to take place in the fall, for the most part, and so Harley and I deliberately went there in October and tried to absorb the atmosphere of the light during that particular time of year. There's a lot of moisture then and shadows aren't so distinct. The light has a nice silvery quality to it and it's warmer. And the leaves are turning.

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The goal was to create a cozy movie with warm tones. A neutral palette was chosen so that skin tones and food would stand out and look juicy. [12]

"We spent some time looking at some of the older French kitchens. Again, we really tried to hold our palette to neutral tones so the skin tones and food would stand out and look juicy. We did put the copper pots in there, so the kitchen wouldn't look too dead."

Calahan definitely approached fur differently. "We've always had trouble trying to light fur and one of the things we've always fought against is to the Kajiya illumination model for the diffuse characteristic of fur," Calahan explains. "It really doesn't work, especially for short fur. Instead we used illumination coming more from the surface of the skin, and we got something a little more appealing that we could control. We have much better grooming tools for the fur than we've had in the past. We got a lot more variety and looks of the fur and how it behaved. With skin, we took advantage of subsurface scattering but, again, it helps to get the local color and shadows to come through."

And what about the wine? "Trying to get the wine to look good was extremely difficult and came down to the 11th hour," Calahan offers. "We worked on it for a couple of years and it kept looking awful and then one day it started working when we needed it to. We used a Merlot as a reference. Not too dark and not too light and fairly opaque."

Again, it was part of the ultimate goal: "I wanted people to leave the theater feeling hungry, she concludes."

Bill Desowitz is editor of VFXWorld.