Creating a Flash Flood in the Desert & Going to 4K to Stitch a Crane and Helicopter Shot Together
“When we first came on the location someone handed us photographs of what it was supposed to look like after the flash flood,” recalls Mat Beck, senior VFX supervisor. “And I am looking at this photograph and asked was like, Ã¢Â€Â˜My god, did they send a location scout here after a flash flood?’ And the said Ã¢Â€Â˜No, that these were actually the pictures taken by Chris McCandless.’ It was a goose bump moment."
On set the sequence called for shots from within the car looking out and shots of actor Emile Hirsch getting tossed around inside the car as mechanical rig whipped the car around to simulate the movement of the waves jostling the car. Shooting under the desert sun added another level of complexity for the effects.
“To be honest there might have been more efficient ways to shoot some of these shots if you were just dealing from the effects standpoint,” says Beck. “Some of the stuff we did might have been more easily done if it was shot on a stage, but then you would have lost some of the feeling that suffused the crew with shooting in the actual place where it all happened.”
Entity shot a bunch of elements of waves and surf, as well as a dump tank for the water rushing towards camera. All those elements, combined with CG work should have made the sequence fairly straightforward. That is, until Entity was sent a curveball.
“The most interesting shot ultimately, just because of its origin, was one in which they had a second camera that was pointed down at the car. [Editor] Jay Cassidy was up on the bluff with a second camera and grabbed a cool angle of the car getting bounced around. It was never originally discussed as an effects shot,” explains Beck. “In the shot you see crew members sitting around, the A-camera mounted on the back, a bunch of dust flying around off the car. We CG’d some water, we stole some elements, moved the horizon, replaced the sky and we put some landscape out there to make the water more turbulent. It was basically a visual effects shot created from whole cloth without any planning at all. The irony was that the only thing that survived that was actually shot on location was the movement of the car as it bounced around and even then we had to CG the back of it because it was covered up by a tarp.”
Making the dusty car look wet proved to be an additional challenge. They replicated the car in CG and then worked on their CG water using Autodesk Maya.
“On the plates the car was completely dry and dust was flying off it as it jerked around and it was our job to make it look like it was wet,” notes Jarra. “Part of that was to have the dynamics of the particles adhere to the surface of the car, and not just to be in a splash form but to make it look like it was wet. A dry-for-wet look.”
And what about the always-challenging VFX task of creating water?
“I think creating water has gotten easier,” assert Beck. “We used Maya for the CG water and different kinds of water for different elements. We used a water physics engine, sprites with water elements on them and particles for splashes. One of the things that really tied it together was splashes that came up off the car, off the rock and between the car and the rock. The layers gave depth to the scene and credibility to the impact. And then the splashes landed on the 3D surfaces of the rock and the car to tie it all together. There was a lot of layering with splashes.
“One thing that was interesting was that in order to give a little depth to the scene Eli put a bunch of bushes out in the distance that allowed us to created eddies. So rather than looking out on a flat horizon you see little kicks coming off the foamy water swirling around those contours and then you have some visual information in the darkness and you get a sense of how big this thing is.”
“A critical thing was that it was shot out of order,” explains Beck. “Ideally you shoot the helicopter first and then the crane move to match it up. But for a number of reasons it was shot the other way around. Pre-vis was really critical. We pre-viz’ed a number of different proposed moves and tried to suggest one that would work both technically and aesthetically. If you look at the last pre-vis and it looks an awful lot like the final. I went up to Alaska and was beating on the Akila guys to make the crane as long as possible to get as high as possible. We had an 82-foot crane that was pulling back from the close-up up as high as it could go. And then we shot the helicopter trying to match the position of the crane on a different day with different weather. So it was our job to match those two together.”
Obviously the crane shot was a lot smoother than the helocopter shot but thre were also differences in position and motion path. In order to smooth out the helicopter shot and to match the cameras, the two shots were transferred at 4K, which allowed them the flexibility to stabilized and push into the shots as needed.
“There was a lot of stabilization of the plates and stabilizing the scale,” explains Marty Taylor, VFX supervisor/lead compositor. “The crane finished below the height of the helicopter and the perspective was different, you saw more of the top of the bus in the helicopter shot than in the crane. This way we were able to lock the two plates together and stabilize and match them. From there figure out what we needed to add as CG elements and matte paintings.”
Because the shots were done on two different days under very different conditions, Entity had to essentially re-create large patches of the landscape.
“One day was rainy and the other day was dry,” recalls Taylor. “On the rainy day all he plants were knocked over and beaten by the rain. On the other shot the plants are dry and standing up. So we had to match that and then we had to make the propeller-wash disappear. The crane is nice and smooth and there’s no wind. Then you get to the helicopter portion and everything is blowing like crazy.”
Once the moves were matched Entity had to create 2D and 3D landscapes, and morph back and forth between those and the real landscape. In addition, Entity FX had to replace a road and production base camp with pristine Alaskan tundra.
“We refer to it as a matte painting but it was actually a 3D reconstruction because it was moving in perspective as the camera was pulling back,” notes Beck.
“We basically took gave the shots a bunch of different looks. We did different contrasts and color corrections and added different style of grain to emulate 16mm or 8 mm. [Jay Cassidy and Sean Penn] chose different looks for different scenes. Some had a black grain that didn’t look like and sort of film stock.”
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