Computer Graphics World

July/August 2014

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j u ly . a u g u s t 2 0 1 4 c g w 6 1 V I S U A L E F F E C T S "The director wanted them to feel like they were in a wind tunnel, and they were," Rahhali says. "There was a ridiculously sized fan and water. They spent all day acting in soaking rain with wind so strong, the water hurt when it hit their skin. I felt for them." W I N D Two CG supervisors at Method – Doug Bloom for eff ects and Blake Sweeney for lighting and animation – managed the teams of artists. Jeff Allen was compositing supervisor. To show the tornado advancing, when the camera is outside the storm drain, the artists created wind blowing across a fi eld of grass and in the trees, increasing the intensity of the storm until we see the mile-wide tornado. "We either replaced trees completely or, if there were many trees embedded in the plate, we replaced enough to create a feeling of wind," Rahhali says. Modelers built a library of trees, construction yard equipment, cars, and so forth. "We mod- eled and textured a version of anything they shot," Rahhali says. "They put black tarps over foregrounds and had the rain and wind machines inside the tarps." Outside the tarps, though, it was a bright sunny day on location in Michigan. "Jeff [Allen] had to do roto, grading, and comp tricks to bring the environment into stormy weather," Rahhali says. "We tracked everything in 3D, and then repainted the sky, replaced trees, and added the wind, leaves, sticks, and other debris swirling around. We had lots of plate prepping and re-projections in [The Found- ry's] Nuke to add CG extensions and blowing trees." SpeedTree so ware helped the modelers create hero trees quickly and bare trunks and branches for multiple trees in forests. "We took the models into [Side Eff ects'] Houdini and created a system to add leaves quickly," Rahhali says. "At render time, we warped the trees and added dynamics." Side Eff ects' Mantra rendered the trees, volu- metrics, and school destruction. Chaos Group's V-Ray rendered individual hard-surface elements. As the tornado steadily approached, the wind needed to increase and the weather become more severe. Rahhali THE TWO IMAGES AT TOP SHOW FRAMES FILMED ON LOCATION. THE TWO IMAGES AT BOTTOM SHOW THE SAME PLATES BUT WITH A FIERCE TORNADO REPLACING THE SUNNY SKY AS SEEN FROM A DISTANCE (AT LEFT) AND IN YOUR FACE (AT RIGHT). " WENT THROUGH EVERY SHOT AND GRADED IT FROM ONE TO FIVE BASED ON WIND SPEED AND THE SEVERITY OF THE WEATHER."

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