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MillimeterStep By Step: Tropic Thunder
Sep 1, 2008 1:00 PM, By Ellen Wolff
“LightWave has some amazing tools for solid body objects,” Breakspear says. “Our helicopter was built to be used full frame. The camera comes pretty close to it, so it's dinged up and the windows are cracked.”
To make the chopper hit the ground realistically, CIS Vancouver simulated smoke and flying dirt and grass. “When you do an explosion and simulate debris, the debris flies around based on physics,” Breakspear says. “But Ben wanted the debris to come towards camera. We worried that it would look too contrived, but Ben knew how to balance the photoreal and the comedic.”
Simulations were done using Autodesk Maya and Side Effects Houdini. And CIS developed a plug-in for Houdini to simulate the mortar explosions that bring down the chopper. “This plug-in affectionately became known as ‘Blow Me,’” Breakspear says. “Our CG mortar explosion was designed to match the practical ones on set. It took eight months to build this thing.”
Rendering of the CG chopper was done in LightWave 3D, while other CG elements were rendered with mental images mental ray and the AIR renderer from SiTex Graphics. Several 2D elements were also incorporated into the scene, including a matte painting of the crashed helicopter. Matte painter Romain Bayle used Softimage|XSI, Adobe Photoshop, and digital-camera images of fire and debris.
Compositing was tricky. “The scene occurs on a sunny day, and there's oily smoke coming out of the back of the chopper,” Breakspear says. “There's also haze from practical mortar explosions going on, so we had to reposition elements, add CG, and then get realistic camera shake and color correction.”
Compositing was done in Shake. “We've imported CG cameras into our version of Shake so that we can manipulate camera shake and depth of field,” Breakspear says. “When objects are flying past the camera, you want a combination of motion blur and depth of field to make it look photoreal. So having the ability to import cameras made a big difference.”
Color correction was done in Shake using software called ana-log, developed by CIS and Deluxe. “We can take plates from our clients and make sure that the data is protected all the way through the process,” Breakspear says. “We've developed the software to do non-destructive color correction. We don't want to burn something into the image that we can't get rid of later.”
Breakspear says the tools used for Tropic Thunder were archived right along with the images themselves. “That way, when we have another explosion to do in the future, it won't take much to reconnoiter plug-ins like Blow Me,” he says. “We could call it Blow Me Again!”
CREDIT ROLL
Director: Ben Stiller
DP: John Toll
Visual Effects Supervisors: Michael Owens, Michael Fink
For CIS Vancouver
Visual Effects Supervisor: Mark Breakspear
Visual Effects Producer: Christopher Anderson
Visual Effects Line Producer: Jinnie Pak
Visual Effects Coordinator: Steve Won
CG Supervisor: Craig Calvert
2D Supervisor: Martyn Culpitt
CG Artist: Dan Mayer
Compositor: John Cairns
Matte Painter: Romain Bayle
Color Correction Software: Ken Hayward
Continue the discussion on Crosstalk the Millimeter Forum.