The Motorcross Sequence
Another sequence that was effects intensive was the motocross sequence. For the most part, the sequences were all real stunts, but the ending where Emmers pulls out two guns and fires at the angels in a mid-air "bullet-time" sequence required VFX from Imageworks.
Mark Stetson: I really admire the work that Mic Rogers and his team did on this sequence. The stunts were such high quality that I almost felt guilty putting any visual effects effort into it. Once people find out that there were visual effects in the shots, people think that most of it is fake. But so much of it was real that it was almost demeaning to do any visual effects on it. Obviously, as the action heightens and approaches near-fantasy, visual effects were needed.
No CG bikes were used in these shots. We pre-visualized the whole sequence but it was all done as green screen composites. Second Unit Director of Photography Jonathan Taylor worked with the camera department, the special effects department and the stunt team to come up with bike rigs that could mount a 35mm camera to the sidecar, a 16mm camera on the motocross bikes and run them through the course. We also made great use of Spydercam aerial cable-rigged camera plates, and a motion control crane, the Image G Bulldog, which we had out on location for several plates.
The big frozen moment "roundy-round" shot at the end of the scene was produced using motion control rigs. Again, this started as pre-visualization and once the shot was laid out, we broke it down to moves that could be shot both on location and on a green screen stage. It became particularly complicated because it turned out in certain instances that the camera crane was in the way of itself and riders. What ended up happening was that the rig used on location had the camera swinging from a central position, but on the green screen stage, the camera was reaching from the outside-in. Because of this, the camera passes were never an exact repeat pass, but it was doing the right thing between the passes and gave us the elements needed to do the composite.
As the sequence gets more fantastical towards the end of the race, we used large speed ups in excess of 1000x. We also had a lot of clean up, paint and comp corrections.