Weta’s Mulan Qi

Disney’s Mulan, the re-imagining of the beloved tale, arrives on major digital retail platforms beginning October 6. It has never-before-seen bonus footage and deleted scenes exclusively in digital in Ultra HD quality and Dolby Audio on compatible devices. Mulan is directed by acclaimed filmmaker Niki Caro. In Disney’s new live-action adaption of Mulan, a fearless young woman risks everything out of love for her family and her country to become one of China’s greatest warriors.

When the Emperor of China issues a decree that one man per family must serve in the Imperial Army to defend the country from Northern invaders, Hua Mulan, the eldest daughter of an honored warrior, steps in to take the place of her ailing father. Masquerading as a man, Hua Jun, she is tested every step of the way and must harness her inner-strength and succeed. It is an epic journey ending in a complex battle to save the Emperor at the new Palace construction site between Mulan and Böri Khan. The story also features the witch Xianniang, who uses her magic to shapeshift in the service of Böri Khan.

Yifei Liu as Mulan

Weta Digital was the lead visual effects facilities on the film, and Anders Langlands was the Visual Effects Supervisor, and Sean Andrew Faden serving as the Production Supervisor. Much of Weta’s work was focused on the last act or third of the film, in scenes involving the Imperial city and the fight at the Palace Construction site.  Weta completed 434 shots for the film. Anders Langlands will be speaking in detail about Weta’s work as part of the upcoming View Conference. His talk will be on Monday, 19th Oct from 9:00 am CET (Central European Time).

In the leadup to the View Conference and to coincide with Mulan being released widely this week we sat down with Anders Langlands to discuss some of the complex issues in environments and staging that Weta faced.

Principal photography began on August 13, 2018, at locations in New Zealand + China, and wrapped on November 25, 2018. Weta sent a second unit team to China to collect background plates and reference material. Their work centered around the Imperial City off Chang’an in China. The team photographed and LIDAR scanned intensively, making this the biggest LIDAR scanned project that Weta has done. One of the issues the team faced was collecting reference before the principal photography had been done, so they had to estimate what sort of backgrounds might be needed once the main unit started shooting in New Zealand.

Today over a million people live in Chang’an, in the film version Weta needed to create approximately 90 square kilometers of the city. Luckily there has been much research done on this ancient area, in particular, a lot of archaeology, from an academic team in Singapore. Weta referenced this and drew on other historical accounts to provide a plausible majestic city. Chang’an comprises 9 districts, laid out in 3×3 grids which were then divided into walled areas. To build the vast Imperial city the team used Houdini. The team took some liberties taken with some elements in the film from a historical perspective as the film is clearly not designed to be a historical retelling of events. “We built in Houdini to allow us to construct the entire city procedurally,” comments Langlands. “So, we wouldn’t have to hand place every building, and yet make something that looks suitable”. The team mapped the city space into different regions via a set of rules.  Some spaces, therefore, became markets or denser living space, and others were built with the assumption that they were for dignitaries, with a higher concentration of wealthy people’s homes and more space. Houdini replied on a modular process that would stack and merge together in ways that were plausible but non-repeating. This set of rules was complex and allowed for variations in terrain that might have indicated watercourses and the natural evolution of a city.

The city was rendered in Manuka, the inhouse renderer at Weta. Langlands who has a very strong personal background in shaders and 3D finds the Manuka spectral renderer “really nice because you just don’t have to worry about whether your colors match or not, – in theory, …it’s really interesting that there are a number of different techniques to try out and then figuring out what the best one to do is. The rendering team we have here at Weta is at the cutting edge of research and the bleeding edge of what’s possible in rendering. It’s really exciting to be around.” Manuka is an end-to-end calibrated system that allows for a very accurate reproduction of many complex materials such as gold, while also matching very closely to filmed live-action elements.  The film was shot on an Alexa 65, which Langlands comments is “a lovely camera with a very big sensor and a gorgeous depth of field.” The DOP Mandy Walker used an older 85mm lens quite often, as it has a rich and complex bokeh, but as Langlands points out, for the last 50 years, technology has been working to make imagery sharper and cleaner, so the team had to work hard to digitally match the “rich and creamy distorted bokeh around the outside of the frame,.. to match the wonderful halo it placed around the actors.” The lens got nicknamed the Qi lens, “that’s all that anyone ever called it, and I’ve forgotten what it actually was!” Langlands jokes, referring to Mulan’s Qi inner strength.  The costumes and props references were shot with a portable 120 calibrated DSLR photogrammetry rig to reconstruct geometry and sample textures.

The team also used a new raytracing version of Weta’s Gazebo real-time render using RTX cards. “Which was really cool because one of the problems that you have with traditional graphics card rasterization pipeline is when you’re dealing with huge amounts of geometry, like an entire city, it problematic. Having to do a full Manuka render just to get any kind of preview can be quite time consuming,” explains Langlands. The new RTX Gazebo filled the gap in terms of being able to get a quick lighting view of the entire city.

For the construction site and Mulan’s roof top run to save the Emperor the principle actors were filmed on green screen. There were three partial sets built in New Zealand of the construction site, “because the tower that they’re on is obviously quite tall that they’re dancing around on top of it, –which has certain practical instrument implications if you want to shoot that safely,” he explains. This was built as two different sections. The bottom section was on the backlot, so a lot of those shots, could essentially be done in-camera with some cleanup in front of white silks. The upper section where a lot of the fight happens was on the main sound stage. There was a third set for wide shots.

Because the set was built out of bamboo, the live-action pieces were difficult to lineup. Additionally, there was a lot of greenscreens but not really enough room beyond the sets for proper separation and this all added to the work of Weta’s talented Nuke compositing team.

Xianniang’s magical transformation or shapeshift is visually only seen strongly in one scene as the director did not want to lean on the effects or make the visual the centre of the narrative. The main transition is early in the film when Xianniang transforms back from being a soldier and the changes to a bird and flies off. This also relied heavily on the comp team as it was shot on location and not on a green screen in a studio. As the shot was in an alley there was no room for motion control so the team had to shoot multiple passes and try and sync the plates to allow the compositor to blend from the male soldier to the witch which happens as the audience is focused on their legs and costume. The result was an elegant transformation that the Director wanted and not the usual particle flashy effects driven solution the director wanted to avoid.

Li Gong as Xianniang

Having matched the plate photography, digital version of the soldier and the witch were created so that the animation of their costumes could bridge the visual divide. A lot of the witches costume is fully digital throughout this shot to make the timing work. “Beck Veitch did the shot, she was one of the comp leads and she did an incredible job getting all of that together. She put it all together, worked out what the constraints were, worked out where we needed to go to CG and what parts would work from the plate photography,” recalls Langlands. “And then once we had that template we could show it to Niki (Caro,) and Sean (Andrew Faden) and get sign off, – then go back, and do the hard work of matching all the live action digitally to execute the digital plan.”

The production had a live hawk on set, Gretel, which was used in a lot of in-camera shots but Weta had to do a CG version and Gretel lost a lot of feathers after the shoot so when the Weta team came back to Wellington, they ended up having to shoot texture reference for feathers with ‘Fern’ the hawk and give Gretel a makeover.

Note that while we spoke to Weta Digital, Sony Imageworks also worked on the mountain attack/avalanche, Framestore provided the Phoenix animation and Image Engine also doing some environment work, especially around Mulan’s home.