WAR HORSE -FRAMESTORE GOES TO BATTLE

During pre-production, the production and Framestore established that the project would need a range of visual effects from paint cleanup to full digital horses but was essential that the work should never be visible.

Detailed Previs
When Framestore’s work got underway, led by VFX supervisor Ben Morris, previz supervisor Josh Wassung and the team at The Third Floor had started developing previs with the director in LA for the film’s key sequences. Ben said, “They created some very detailed, engaging previs that not only helped us plan for the VFX challenges, but also allowed the other departments to see what the major scenes were going to involve. As with all aspects of the project, it was collaboration and shared responsibility between departments that allowed Steven to achieve so much of the film in-camera.”

Ben and his team from Framestore were in Devon shooting for three weeks. The VFX team were on-set every day of shooting. Ben and Steven Spielberg would discuss all possible options for achieving shots in-camera or with fairly simple VFX. Steven tended to prefer more traditional and, in some cases, more time-consuming techniques such as multi-pass crowd replications instead of immediately turning to CG. Ben said, “I think this approach really pays off in the film, as these shots naturally have a level realism that is in keeping with the rest of the film.”

In-Camera Battles
Ben found Steven was decisive and dynamic on set, shooting quickly and always thinking two or three set-ups ahead of the shot being filmed. He made a cut every day with the editor Michael Kahn, so he knew exactly how much of the sequences had been covered at any stage. This way the crew were never more than a day or two ahead of the edit and knew if pickups were needed before changing locations.

Shooting the battle sequences with Steven and DP Janusz Kaminski was especially exciting. “As planned, the daylight trench attack sequence is almost completely in-camera with practical stunt and SFX work supervised by Rob Inch and Neil Corbould,” said Ben. “We enhanced the expansive No Man's Land set in a few shots, extending the deep background with further trench landscapes, burnt trees and smoke elements. We also added gun muzzle flashes in numerous shots.”

“While shooting at Narracott Farm we did get involved in the scene involving Joey and Albert ploughing the barren field near the farmhouse. For safety the plough that Joey pulls often had a cabled winch system attached to it for shots showing it actually cutting the soil. The cleanup work was mostly 2D based but some of it involved complex occlusion of Albert, Joey, the plough and the cut furrows of soil. The compositors often had to patch through their fixes with many layers of projected texture using 3D camera tracks, working in Nuke and Silhouette. For wider shots we also painted out horse wranglers, harnesses, rain stands and added rain elements,” Ben said.

A shot of Harold, a goose, chasing intruders from the farmhouse was harder than expected when the trained goose failed to perform. For the main shoot, the actors performed the scene without the goose, and then Ben’s team returned to the same location a few days later and managed to capture shots of the goose chasing his trainer running towards the gate. Without motion control passes, both shots were tracked in Nuke and the separate plates of the actors and goose were then aligned to create the final shot.

As the British Cavalry approach the German line at the edge of the forest they suddenly realise their mistake and are killed by a hidden line of machine guns. Steven had decided to not to show riders and horses being gunned down and preferred to use shots of riderless horses, jumping over German gun positions, to tell the story. Framestore’s team worked with the horse trainers and the stunt team to build a system of horse lanes with posts and tape to resemble electrical fencing. It safely prevented the free-running horses from straying off course, but needed weeks of painstaking frame-by-frame paint work in post for the five or six shots in the sequence.

Because the production wasn’t allowed to fire the machine guns during shots with real horses, Framestore added smoke and muzzle flashes using 2D elements shot later on. The team learned that the machine guns used in the film were real German guns from WW1, possibly used in action. Ben said, “At the end of the sequence a crane shot pulls back to reveal the devastation caused to the British Cavalry during the attack. For this shot we extended the numerous practical dead soldiers, horses and burning camp with 2.5D matte painting.”

In many shots of Joey and Topthorn, another horse, pulling a heavy cannon up the hill, the artists had to paint out a large winch system used to pull the practical cannon. As the horses get to the top of the hill Steven wanted to reveal the true horror and scale of the devastation caused by the trench warfare in WW1.

“For this shot we filmed two practical cannons firing from two different camera positions at the same location in Bourne Wood, giving us plates to build the final shot of four cannons firing over the vast battle landscape,” Ben explained. “In post we had to separate the cannon plates into individual cannons for timing purposes, compounding the complex extraction of practical smoke from the forested background in the original plates.

"Working from a concept design by Kevin Jenkins, the matte painters Dave Early and Joseph McLamb painted the expansive battleground of devastated towns, roads and rivers for the comp team to integrate with the foreground plates and layers of smoke and fire. Steven wanted to see the foreground cannons firing and sustain the shot to show the massive distant explosions of the shells landing on the horizon. Rather than generating CG explosions we shot a series of high-speed, practical explosion elements and composited them into the shot.”

Joey finally makes a heroic escape by jumping over the tank. They tried to shoot the action with real horse stunts performed in-camera over a stationary tank covered in flat safety rostrums, and shot several different versions over a number of days. But Steven decided that shots look too static, and wanted the tank to keep moving. When time ran short they finally opted to use a CG horse to achieve the shots.

The artists used synchronised, multi-camera photogrammetry data and a flat lit texture shoot to model and paint the CG horse based on a combination of the two 'hero' horses who played Joey in the film. The cannon harness and tack Joey wore was modelled from photographs. Modelling tools were Mudbox and ZBrush, with Mari and Photoshop for texturing. CG supervisor, Mike Mullholland handled the horse build and rig, using in-house tools to create underlying skin and muscle movement. To light and render the model, hair and short fur Framestore’s PRMan shader library and fur system were used.

Lighting reference for the shots was based on HDR environment maps captured on-set using a Canon 5D, 8mm Sigma fisheye lens and Promote Controller. The final lighting and renders with multiple AOV's were rendered in PRMan and brought together in Nuke.

Over the Trenches
Later on in the story Joey runs behind German lines under attack from British soldiers and must jump over one of the trenches, requiring complex VFX shots combining three real horse plates and two sections of CG horse animation. They studied the previs to determine where they would need to use the CG horse, as in the first shot when the horse misses clearing the trench and hits the far wall, falls to the ground and gets up before running away.

The start of the action was shot as an empty plate into which we would comp a 2D element of a real horse. The master plate camera was mounted on the back of a quad bike with a remote stabilised head. As soon as the operator made his reaction and pan from right-to-left, the quad started its high-speed run down the occupied trench. “At just the right moment we signalled for a horse ridden by a grey suited stunt rider to start its run along the left edge of the trench. After a few rehearsals, we managed to reveal the horse and rider as the quad bike hit full speed down the trench,” said Ben.

“Then an SFX rigged practical shell explodes directly in front of the horse and rider, causing it to react naturally and ride safely out of shot. At this point the camera panned right following a non-existent horse to meet practically rigged sandbags which fell into the trench as if a horse had hit them. The plate ended revealing the 'empty' bottom of the trench with a group of German soldiers looking on in surprise.” Once the A plate was captured, the camera was mounted on sticks in the position the quad bike had stopped at, where a different horse was trained to get up from a lying position on command and gallop off down the trench.

Alignment Issues
As soon as the plates arrived at Framestore, the compositors made a slap comp of the live-action elements to check alignments, timings and horse performances. Ben explained, “There were inevitably slight alignment issues between the separate plates, German soldiers overlapping at the transition point and lots of cleanup to get rid of lighting and safety rigs. Having camera tracked both plates and aligned them globally in our 3D trench survey, we passed the A plate over to our paint and roto team to start removing the grey suited rider.

“The trackers also calibrated an array of witness cameras we used while shooting the sequence – three HD cameras, genlocked to the 'hero' film cameras and two free-running Arri 435's, just to be safe. As soon as the witness array was calibrated we started body tracking the entire run down the edge of the trench to the point where we would transition to a CG horse after the explosion.” For camera tracking they might use 3DE, Matchmove, boujou or Nuke, depending on the shot.

Once they started to animate the horse in Maya, jumping, falling, they decided they would need to retime and re-rack the camera move to create a realistic horse animation, continuously updating the scene with refined body tracks and camera moves. Once the animation was working well, they rapidly composited the shot together for a first review, using lighting renders that had been prepared in the meantime. When they played it for Steven and the editorial team in LA, they met a very favourable response.

CG Jump
However, Steven immediately remarked that the first real horse jump didn't have the same impact as the rough comp of the CG horse landing. “Over the next few weeks we refined the CG horse lighting, animation and comp,” said Ben. “We replaced the entire side of the ridden horse with a CG saddle and blanket and ultimately replaced most of the practical sandbags with CG ones that integrated better with the animation of the horse. While we worked to make that first, real horse jump element look better, animator Laurent Benhamo secretly worked late and animated a version of CG horse jumping the trench to open the shot.

“When he finally showed me the animation I thought it looked great, so we rendered it and passed it on comp. At the next review Steven again loved the shot and said the new horse element at the start of the shot looked more realistic and majestic. It wasn't until the following review that I actually told Steven it was a CG horse.”

No Man’s Land
Perhaps the film’s most suspenseful scene is when Joey races through No Man's Land, under shell fire. To ensure the safety of the horses, many of the shots were filmed with stunt riders on Joey which had to be painted out. Saddles and body sections were replaced with CG elements. The No Man's Land set was enormous and needed numerous lighting cranes, which also had to be painted out.

Eventually, Joey runs through a series of barbed wire barricades strung between Belgian gates. He drags the gates with him as the wires wind tightly around his body and only stops when the gates hit an obstruction. The horse would be replaced of course, but the team needed reference of the running horse, captured with the array of witness cameras. Broken gates were also dragged behind quad bikes and shot as further reference for the artists to re-create the run accurately. All barbed wire used near the live action horses was break-away plastic, and the wires were not permitted to trail from their bodies.

Before starting these shots, Framestore’s art department painted various concept frames for key shots of the tangled wire and the effects team started rigging the wires according to the designs the director approved. The artists worked on the sequence in Maya and Houdini, and used N-Cloth with the Framestore proprietary fBounce dynamics engine to wrap trails of procedural barbed wire around the CG horse model, which was body tracked. The wires’ behaviour could be adjusted to match the springiness of the real wire in the reference. The compositorscompleted the shots with 2D elements plus CG debris and dust passes.