Close-Up on Legion: Gabriel's Wings

There have been a number of articles describing how Spin VFX created the visual effects for the Screen Gems action thriller, Legion.  While they provide a really good overview, they don't cover any particular topic in detail.  I thought I'd give you a closer look at exactly how it was done, by breaking down an iconic shot from the film.  Along the way I'll talk about some of the challenges we faced while breathing life into Gabriel's computer generated wings.

Original Plate, Clean Plate, and Final CompositeThis is one of the shots that defined the look of the wings, and is one of my favorite shots from the diner fight sequence.  Gabriel (Kevin Durand) flies towards camera with a diving attack on Michael (Paul Bettany).  Inspired by the comic book superhero, this shot was often referred to as, 'the Thor shot.'  We started by rotoscoping the actor's upper-body, removing the wire rig, and replacing the missing ceiling tile which had been removed to accommodate the rig.  The matchmove department tracked the camera move, and object tracked the actor in order to 'attach' the wings to his back.  Based on 3D cyber scans of Kevin Durand, lead modeler Erin Nicholson built a low-resolution version of Gabriel in Maya to act as our digital stand-in.  Paying special attention to the upper-body, the layout department, led by Phil Dakin,  solved the camera and object tracks using PFTrack, and placed our Gabriel proxy model into the scene along with our tracked virtual camera.  Low-Resolution Proxy Model of GabrielAnimators carefully matched the actor's movements, which provided a solid foundation for the wing animation.  Animator Jongju Lee was assigned the task of providing the powerful yet graceful 'hero' wing animation.  Finally, rigging supervisor Glen Chang, ran a character effects pass to simulate the subtle effect of air rushing across the surface of the wings, causing the feathers to ruffle.  This added layer of detail really helped bring the wings to life.

HDRI Reference StillsOnce director Scott Stewart had approved the animation, the scene was passed to the lighting department.  Using HDRI reference photos of the set, lighting TD Paul George built a rig which accurately reproduced the physical lighting environment of the diner.  One of the challenging aspects of the wing design was striking a balance between natural looking feathers, and armoured ones capable of stopping bullets.  The small feathers along the top of the wings were softer and more organic, while the larger primary feathers at the wing-tips narrowed into hardened steel blades.  The wing textures were distressed, scratched and engraved with markings similar to those found on Gabriel's armour.  Ultimately, the task fell to the compositors to fine tune the final look and feel of the wings.  I used this shot to develop that look, and then built templates for the compositing team.  In order to give the artists maximum flexibility, we rendered multiple CGI passes as layered EXR files, Diffuse, Color, and Specular Lighting Passeswhich were later combined in Fusion to produce the final composite.  Among the layers were a number of utility channels including, a z-depth pass, various isolation mattes, and even a special iridescence pass, which created a subtle oily refraction effect on the wing surface.  Having this level of control presented it's own set of challenges.  For instance, how could we ensure that each artist produced a consistent look, allowing the shots to edit together seamlessly?

Fusion Template and Wing Macro Tool

By automating the process, we could ensure consistency among the compositors, and perhaps more importantly, we could build the individual shots much more efficiently.  I wrote a Fusion script, which both the lighters and compositors used to quickly build composites based on pre-defined templates.  They could simply select a sequence code, shot number, and lighting version, and the script would load the corresponding plate and CG wing layers into a basic comp.  The individual passes were piped into a custom wing macro tool, giving artists fine control over each of the components.  But, by limiting the artists to a fixed set of controls, we maintained continuity from shot to shot.  Since the roto and clean plates were completed ahead of time, once the lighting passes were rendered, we could quickly generate comps in a matter of seconds.  From there it was up to the compositing artists to integrate the wings seamlessly into the live-action plates.

Shadow Pass and Normal-MapThe digital Gabriel model was also used to cast shadows onto the wings, helping them to feel connected.  Atmospheric elements such as dust, and smoke were layered over the wings to provide interactivity with the environment.  Finally, a surface normal pass could be used to make last minute lighting adjustments in the comp, giving artists even more control.  Having this level of automation and control proved especially important during the final sequence of the film, where Michael returns to face Gabriel in the final battle.  This meant that the compositors had to integrate two sets of wings instead of only one.  Click below to watch the final shot, and be sure to check out my reel for more of my work on Legion.

Comments

[Rahul]

Thanks for the detailed breakdown Eric. As you have stated most of articles these days just give a general overview so its always good to get some really deep insight on a particular shot.

If you don't mind can you please elaborate on usage of iridescence pass to get the oily look.

[Eric Doiron]

Rahul,

Apologies for the delayed response. We multiplied the specular pass by a special color pass which tinted the specular channel as light passed across the wing. Ultimately, the director and visual effects supervisor didn't respond well to the effect, so it was used sparingly and mostly in the bright exteriors.

Thanks for the comment.