Imageworks Making a Mountain Avalance Battle Escape For Mulan

In Disney’s Mulan, filmmaker Niki Caro brings to life the epic tale of China’s legendary warrior. One of the main visual effects suppliers was Sony Pictures Imageworks.

The Imageworks team led by VFX supervisor, Seth Maury, animation supervisor, Julius Kwan, compositing supervisor, Sandra Balej, and VFX producer, Jarrod Nesbit. The team were tasked with delivering sequences from the epic battle sequence in the third act of Mulan. The epic battle was shot in a valley on the South Island of New Zealand. The plates had a lot of natural environment in them. Artists had to add a mountain that would be the site of the major avalanche and also the foothills leading up to the mountain. They added mountain extensions including 2D and 3D features to the battlefield itself along with rocks and steam vents to give the appearance of thermal pools in the ground. Imageworks was tasked with producing 20 to 30 hero shots of the avalanche sequence which was one of the biggest visual effects sequences in the movie. The SPI artists broke down the avalanche into two different types: wide establishing shots, and more immersive shots.

To achieve the avalanche effects, Imageworks built a new system inside Houdini called Katyusha, for simulating snow and ice.

In addition to going with a volumetric approach, the team committed to simulating many passes as a way of ensuring flexibility in compositing. The team rendered using SPI’s in-house version of Arnold.

One hundred percent photorealism was the ultimate goal. SPI’s artists referenced tons of real avalanche footage. The artists used real-life as a starting point but for creative reasons, sometimes artists needed to slow down or accelerate the pace of the avalanche.

Digital Horse Power

Mulan’s escape required Imageworks to add two different types of horses to the film. One was Mulan’s Blackwind, which was built and detailed employing upgraded tools so that it would hold up close to camera. The CG Blackwind was a very detailed model that used a new muscle sim system under the horse’s skin. The dev team also created a new hair solver called Fyber that was more interactive and much less data-heavy so that the artists could iterate faster.

Production side VFX supervisor, Sean Faden, encouraged Imageworks to create what he called the ‘Pepsi Challenge,’ running slow-motion footage of Mulan on Blackwind, riding through a canyon, side-by-side with the CG Blackwind. Artists rotoed the footage of Mulan on the horse, matched the lighting conditions, and matched the CG horse to that horse.

Artists based lower-res background horses on the Blackwind model, varying coloring, manes, tails and other characteristics. They created as many variations as possible to make sure that crowd scenes never looked repetitive.

The CG Blackwind is seen in battlefield shots too chaotic and dangerous to be shot with a real horse and in shots in the following sequence, in which Mulan races to catch up with her friend and ally, Chen Honghui (Yoson An) when he is swept up in an avalanche. For this sequence, Mulan was shot on a green mechanical buck and replaced that with a CG horse. Its face, mane, and body are right in front of the lens in some shots.

Article content ref from: www.fxguide.com