The stand-in proxy F3 cars, the picture cars, the tracking and matchmoving, and more. An excerpt from issue #43 of befores & afters magazine on ‘F1’.
Below is a lengthy excerpt from the latest issue of the magazine, which is fully dedicated to F1. In the mag we go in-depth with the VFX team on the film, including production visual effects supervisor Ryan Tudhope. Read on to learn specifically about the re-skinning work.
Re-skinning was a term utilized during the making of Top Gun: Maverick, where real, flying stand-in jets filmed for aerial scenes were ‘re-skinned’ to be the required jets for the story of that film. That’s effectively what happened in F1. For this film, a range of techniques were used to represent cars on the tracks. These included shooting with specially built picture-ready APXGP cars, shooting with black F3 cars that acted as ‘doubles’ during the shoot, and also using cars featured in the broadcast footage. The VFX team scannned and photographed the APXGP car on a large turntable built by SFX, which could be spun in front of a camera. Then, depending on the shot, cars would be re-skinned with the required liveries. First, of course, Framestore needed to build digital F1 car assets to undertake that task.
One of the challenges, here, was getting access to real-world F1 vehicles for reference and textures, as Framestore visual effects supervisor Rob Harrington notes. “The competitor F1 cars were competing in an active championship and, in a sport like F1, each car is a secret design where, yes, you can look at it, but equally a team would not let you walk up to it with a tape measure as it’s legitimately that team’s design which they’ve spent millions of dollars on. Luckily, however, Ryan and the team had press-level access during the race weekends, meaning they could get great ad-hoc photos in the pits and on the pre-start grid to make up for not being able to scan cars or have dedicated photo sessions. Mind you, even if we could scan them, they’re not typically ‘scannable’ objects with their clean, curved surfaces and reflections.”
Framestore’s artists utilized precision-tracking and photo-modeling techniques to build the assets. “First we would track stills from Ryan’s grid walk photos against the production’s really high resolution textured LiDAR. The photos texturing the LiDAR were 9.5K stills captured by drone and would give enough resolution to let us even identify particular stones and oil patches. Once the scenery was tightly tracked we would move onto the cars themselves, creating a point cloud of the clearly-defined trustworthy points on each, say for logo corners, screws, etc, and let the software solve their positions with only a few constraints added by us. We would then model through these points and start deducing the complex curved shapes between these points.”
“Obviously,” adds Harrington, “deducing isn’t the same as knowing, so we would fine-tune our surfaces by projecting the photo sequences back on the model and viewing the result from a third point and, as you scrubbed the time line, the less the image swished and swirled around, the better you knew your end result was. It worked well as it was something you could just do live and immediately in the viewport without resorting to QCs and renderfarms. If we were not sure about a point, we’d move it up 10mm and scrub again. It was so important that we got this as-right-as-possible as whilst the FIA regulations give essentially ‘bounding box’ volumes for F1 cars to exist within, very few useful dimensions are actually specific, and, very broadly speaking, if our car ended up being 5% too big then it would solve 5% too far away, therefore we needed to be sure as data would allow that we were happy with our versions of these special cars.”
As the car builds progressed, Framestore quickly discovered another challenge. The liveries on the cars and helmets of the divers changed over almost every race. There would ultimately be hundreds of shots in the film where Framestore changed or added other teams to shots, say in a piece of broadcast footage that had the desired action, but the wrong cars for continuity. “We might need to change a Red Bull into a Ferrari, or a McLaren into an Alpine,” remarks Tudhope. “We misjudged how often they changed their liveries, so we had a lot more variance on these cars than we thought we would have, but whenever you see those cars in a particular race, they are in the perfect exact livery right down to their helmets of the drivers.”
During filming, supervising stunt coordinator Gary Powell established the choreography while driving the F3s. Sometimes the APXGP cars were also driven as stand-in cars by stunt drivers to play the other teams, which then of course had to be re-skinned. “The idea was always to shoot something,” observes Tudhope. “We were trying to give the camera operator something to follow, even if we were replacing it, and even though one or two of the cars might be missing from it, or even though they aren’t the correct cars, and even though there’s no crowds or signage—we’re still out there trying to create a foundation for a shot. That, in my belief, is why audiences walk away from this type of film with F1 or Maverick convinced that it’s more real than not.”
Re-skinning with these digital car assets then depended on the needs of the shot. When the APXGP cars needed to be re-skinned, for example, consideration had to be made for the fact that they were effectively F2 cars. Explains Tudhope: “The chassis was stretched a little to try to make the wheel base match an F1 car, and then it was skinned over in a real sense from Mercedes AMG with body work that was much more resembling an F1 car than an F2 car. But the engines under the hood were effectively F2 cars. They were incredibly valuable because they were our picture cars, obviously, and we only had six of them. So putting them into really dangerous situations such as spinning them off into the gravel where the gravel could get all up into places in the car that was not good, or the body work could get damaged and so forth, it just wasn’t worth it.”
“So,” says Tudhope, “we did a lot of those stunts with the F3 cars, which were much more affordable. They’re quite a bit smaller, but despite the fact that the size was off, it still gave the camera operator something to track. It gave us dust and debris. There are shots, for example, in Hungary where Sonny drives through a sign and it explodes under the track and he’s trying to create a yellow flag. We did that with the F3 car and re-skinned it as our APX car. This just meant a lot of the death-defying shots you see are real stunts occurring, but with the wrong car.”
In re-skinning, Framestore’s meticulous tracking work came into play in a major way, as did a range of other CG work and compositing. There might be times, too, when plate footage was re-purposed to bring cars closer to each other for more dynamism or jeopardy, for example. “We did various things to the plate cars depending on what was filmed or how they were shot,” states Harrington. “If it was a straight re-skin, i.e. ‘change this APX car we shot here to a Haas car’, then we would do a good chunk of in-painting to fix the overlaps whilst trying to keep as much of the real plate’s shadow as possible.”
“For other shots,” says Harrington, “whilst we would not strictly re-skin the whole car, we would tidy-up sections of them to help remove things like camera gear, where you might need a CG side pod or replacement scuttle-area, or replace areas of the car so we could fix environmental reflections for continuity. Many of the large colorful sponsors around the track disappear in the days after the real races had finished, which is often when the film work would start. Nuke would also pick up some of the lifting here with pure 2D effects to change the colors of the signage reflecting into cars, for example, Qatar Airways maroon to Pirelli yellow. At the end of the day you would always try to keep as much of the real car as possible and try to work with the panels gaps which matched well between the real APXGP car and its CG version.”
Most of Framestore’s shots were based on a real plate of a real car doing a particular piece of action. This meant that the vehicle’s overall motion would come from tracking. Extra work was required, however, to fully realize the racing cars. “Tracking would only give you the ‘body motion’, as there’s no way you’re tracking the suspension,” notes Harrington. “It’s at this point that animation would take over. At a base level, anim would run a pass with the rig to take care of wheel contacts and tire squash, but they’d also go and dial in the driver’s performance and add the deformation as you see with the flexing on the real cars.”
“What also becomes very apparent on high-resolution car-to-car shots is the amount of sub-frame vibration you get when you’re filming at 24 fps,” continues Harrington. “You could look at the plate and all the highlights would go through phases of ‘squiggling’. This is something we would have to add to our re-skinned cars to match what was in the plate. Anim would envelop in some interesting sub-frame noise which gets picked up by adding a lot of sub-frame steps to the anim caches, and if we still needed more—as some plate examples were extremely lively—then we would embellish it with Nuke.”
