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Posted Sep 17

Gotta go fast: creating supersonic motion blur effects on ‘Sonic The Hedgehog’

by Will Earl
Gotta go fast: creating supersonic motion blur effects on ‘Sonic The Hedgehog’ by Will Earl

How do you recreate the effects and moves of an iconic video game character for the big screen?

MPC Head of Optimization Will Earl lent some insight into how the studio created the effects to show Sonic’s incredible speed when they provided the visual effects for 2020’s Sonic the Hedgehog.

For creating Sonic’s groom, MPC once more relied on its proprietary groom software Furtility while lighting and rendering were accomplished using the normal pipeline of Katana and Renderman, respectively.

There were a number of challenges for this movie, many relating to Sonic and his speed. Sonic moves very fast, so there was going to be a lot of motion blur with a ‘blue streak’ effect behind him.

In addition to Sonic’s speed, there would be times when he moves so fast, there would be a ‘supersonic’ effect where we would see more of the character’s actual movement within the motion blur effect. And for some shots, we’d also see multiple Sonics with a motion streak between each action or pose.

“We needed to provide the artists with more control to sell Sonic’s speed, so that it wasn’t just a big blue blur on screen,” explained Earl.

MPC Film had created a similar effect on a previous movie to create ghost effects. For that project, the intention had also been to provide the artists the means to artistically control the motion blur through a tool called GhostTrails, which was originally developed by FX Lead Nigel Ankers.

“The basis for the technique is based in still photography when taking a bulb exposure,” Earl said.

“For me, the inspiration comes out of night-time skateboard photography, where a long exposure is taken and then a flash is fired to capture the skateboarder frozen in time. This captures the high-speed at which someone is moving through the use of motion blur but also freezes the action in time so that movement can be understood by the viewer.”

Looking back to a previous project and the tooling seemed a good place to start and see what could be repurposed.

The GhostTrails tool was implemented as a Giggle script and used inside Foundry’s Katana.

Giggle is MPC’s own extension of the LUA scripting language and a component of Muggins – MPC’s 3D Library. The Giggle scripting component of Muggins makes it easy for DCC agnostic tools to be written which can be then used in applications such as Maya, Katana and Nuke.

For usage on Sonic, extra work was required to improve the memory efficiency when dealing with larger number of frames and also for it to work with Furtility, as previous usages had only worked with polygonal meshes and subdivision surfaces.

“The tool itself combines multiple time samples of Sonic’s position across multiple frames, then uses weights to determine which time samples contribute to the final effect,” Earl said.

“For example, we can weigh the effect in specific areas in order to keep Sonic’s face in focus. We can further modify the effect by displacing those positional values in time using procedural textures such as 3D curl noise in order to add turbulence to the motion.”

Why Katana and 3D?

It was possible to achieve the type of effect the team was looking for in 2D. However, 2D can be limiting. On the other hand, Katana, which is used for the lighting and rendering pipelines, allowed the team to keep everything together – camera, lighting, animation, and rendering – when needed.

Earl explained other advantages of using Katana.

“The effect becomes more physically correct,” he said. “You get interesting variation and shapes appearing in the motion blur from the animation of Sonic that you wouldn’t get with 2D techniques. There are shots where the camera dollies around Sonic and you get this nice perspective shift on the trail. You can see this when he’s running on the Great Wall, as he throws the ring ahead of him and dashes past the camera.”

Because the animation is always the base for the effect, there are moments where Sonic can be seen doing multiple things simultaneously. Using the tool, it is possible to create motion blur that blends between specific key poses of Sonic’s animation.

When Sonic runs very fast, he generates lightning that can be used to illuminate his environment. When he does a spin dash, you can see in places the motion blur is emitting a light streak behind him.

Since the rendered effect is based on the animation, the lighting artist would need control over the effect. Katana provided the best of both worlds. – thefocus.com

Photo from Paramount

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