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Way back in 2001 when Mike, Sulley and a colorful cast of characters made their big-screen debut in "Monsters, Inc.," Pixar had some major challenges and technical breakthroughs in the area of fur -- the complexity of the way it moved, was lit and groomed -- and clothing simulation, most notably Boo's t-shirt. At the time, the ultra-hairy Sulley was so complicated and required so much rendering that the filmmakers were restricted in their desire to add other furry creatures. Now, with "Monsters University," Pixar's technical wizards have raised the bar again, taking on several new challenges to make it their most ambitious film yet in terms of lighting, simulation and rendering. Furry monsters abound, the new approach to lighting gives the film an art-directed sense of realism that adds to the experience.

To give a sense of the enormous scope of the project, "Monsters University" took 100 million CPU hours to render, which is equivalent to 10,000 years for a single computer -- the most in Pixar history. On average, each frame (if rendered on a single computer) would take about 29 hours. Pixar's render farm (the network of computers and processing units) roughly doubled in size from what it was on "Brave" to accommodate the needs of the production. Additionally, each computer was turned into a multiprocessor (with 12 processors in each) to allow shots to be broken up and rendered simultaneously on different machines using multithreading.

One of the biggest innovations in the creation of "Monsters University" was Pixar's adoption of a new lighting process called global illumination (GI), a revolutionary approach to lighting that Pixar's technology team elaborately evolved to give the film a striking visual palette. Global illumination allows the filmmakers to use area light sources -- instead of potentially hundreds of individual lights -- to give a more accurate physically based and realistic effect. One of the major benefits of this approach is that the filmmakers are able to get a very quick and early sense of what the final lighting will look like, instead of waiting until the end of the production process as was traditionally the case.

Chris King, global illumination lead for the film, says, "To light a computer animated film, we simulate the physics of light in the scene. In reality, light enters then bounces around infinitely off all the surfaces in the scene. That is impossible to compute so we have simplify the problem somehow. On this film we removed simplifications we used in the past and simulated lights and surfaces much more accurately."

Producer Kori Rae adds, "The global illumination initiative at Pixar was started by three very talented guys at the very beginning of the film who came to me and asked if they could give it a try. They had just six months to come up with something that they could formally present, and they did it. It was amazing. The end result is more beautiful and realistic lighting that perfectly suits the college setting. Plus, we found a more satisfying experience for the production team because they had a sense of lighting earlier in the production pipeline that allowed them to do great work under strict timelines."

Veteran Pixar technical genius Bill Reeves (the second employee ever hired at Pixar and an Oscar-winning pioneer in the world of computer graphics), Jean-Claude Kalache (DP, lighting) and Christophe Hery spearheaded the GI effort on "Monsters University" with help from Chris King, software VP Guido Quaroni and a team of experts.

Kalache recalls, "At the end of 'Up,' I had a 16-page document of notes about things that I wanted to improve, things that I wanted to research and things that I wanted to learn about. One thing that struck me was how complex our lighting setups had become even when we were trying to produce very simple imagery. One of the main projects that I identified was global illumination. When I found out I was going to be on 'Monsters University,' I went to Guido and Kori and proposed taking some time to figure out how to make our lighting setups simpler. Bill Reeves was also pursuing an interest in this area and when he joined the production, we proposed researching GI together. Christophe Hery, who was an expert in lighting at ILM, Jacob Kuenzel, a Pixar technical director, and Chris also joined the team. We knew that the long-term benefits of GI would be tremendous. At the end of the day, it makes a lot more room for the lighter to be creative and artistic, while taking away many of the redundant technical steps they were doing."

"We wanted to try a new approach to lighting for many years," adds Reeves. "What's changed is that computers are now faster and we're smarter. GI is a major re-think of how things work. It's more intuitive and natural, and it allows us to use just a few lights to get a really rich environment. GI lets you light a scene in a day or two, instead of two or three months. For Pixar, GI is definitely a revolutionary step. We had to learn to work differently, but the rich results are spectacular."

Alex Kolliopoulis, rendering supervisor, explains that in order to solve the challenges of GI, Pixar had to first come up with a new way to allocate computer resources. "Global illumination has basically doubled the time and quadrupled the memory requirements for rendering," he says. "We had to come up with a way to multithread the work, which meant turning our computers into multiprocessors. Rather than having one render per core, we'll spread one render across multiple cores. In general, we are using four threads for our heavier renders, which means you have four cores dedicated to one render of a frame. It comes back roughly four times quicker, because it has four times the amount of memory available to it."

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