In 'The Nutcracker and the Four Realms', young Clara discovers an unexpected world of heroic mice, living toys and immense, snowy fantasy landscapes, hidden somewhere within her godfather Drosselmeyer's house. The story is based loosely on the famous Christmas fairy tale 'The Nutcracker and the Mouse King' written by German Romantic writer E T A Hoffmann. The film features beautiful visual effects work that relies on heavy use of blue and green screens on the sets during production.
“Because 'The Nutcracker' had so many scenes shot against blue/green screens that needed to be replaced with our virtual world, one of the first things we did was look for a pre-visualisation system,” said Max Wood, the production VFX Supervisor. “First, it would help the director to frame his shots more accurately – we didn’t want to shoot blind and find out later that we’d cropped the top of the palace off. We knew it would save time and money in post to have a better idea of the geography while on set.
“Second, it would give the post production teams a great head start when it came to production screenings to have a representation of the backgrounds while the final VFX were still being built – people would be able to understand what the movie would look like, and not need so much explanation.”
As a VFX Supervisor at MPC, Max had previous experience of receiving data from pre-vis systems but had never used one on set, so the team tested several different systems, and then chose Ncam. “All the systems we tried had pros and cons, but Ncam had the best all round functionality. We also found it very flexible and it seemed to be the most reliable. Most important, it wouldn’t impact on production times - it was important that factors outside the direct control of the VFX team did not interfere with using an accurately tracked, live set extension.”
For example, during the testing period, the team looked at a system involving an on-camera device that continuously monitors hundreds of reflective disks applied to rigid points around the set. The system worked extremely well, but the lighting department announced plans to cover the entire ceiling in massive silks. These would block the disks in their original positions, and the disks couldn't be applied to the silks as they are not rigid. Ncam, on the other hand, is self contained and does not have these kinds of restrictions.
The ability to make CG geographical changes on the fly was another major factor for the VFX team. “We knew that our pre-vis landscape matched to the art department layout, but also knew from experience that production design decisions can change very quickly while filming is underway. The flexibility of the Ncam set-up assured us that it would be possible to make quick changes.”
Pre-vis Asset Preparation
The system was primarily used for set extensions that ranged from palace walls to vast landscapes going off into the distance with waterfalls and rotating water wheels. The pre-viz assets to represent those elements – which were delivered as 3D scenes created in Autodesk Maya - were supplied to the Ncam team well before the shoot got underway in order to prepare them for use live on set.
“We tweaked the assets to optimise them for use in the Ncam system, for example cleaning up and streamlined the topology of models, removing non-essential detail and making sure that the textures were of a suitable resolution. The files could not be so big that they slowed down playback to less than 24 fps,” Max said.
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