By Ian Failes
Sony Pictures Imageworks ‘aint afraid of no ghost, in fact, the visual effects studio made a whole bunch of ’em for Paul Feig’s Ghostbusters. And now you can too with these step by step guidelines from visual effects supervisor Daniel Kramer into how Imageworks used its strong VFX artistry and technical might to make a myriad of ghostly scenes for the reboot of the classic franchise.
How to Conjure a Ghost in 10 Easy Steps
Step 1. Many of the land based ghosts were filmed on set using real actors covered in LEDs to both illuminate the environment and to provide self illumination. Of course that came at a cost, there was an awful lot of paint work on this movie to remove LED cores, supporting wires and straps from the photography but it did provide a lot of interesting lighting effects.
Step 2. We’d then roto-animate a cg version of the actor to match the motion which gave us internal organs, bone and muscle correctly tracked in 3d space.
Step 3. All of these layers were rendered as volumetric objects with internal illumination, generally leaving the skeleton as a dark occlusive element.
Step 4. For many of the ghosts we also built full cg costumes allowing us to provide an ethereal weightless motion to the clothing and we’d allow the internal lighting to bleed through the cloth in thinner areas.
Step 5. All of these elements were pulled together and combined in Nuke (compositing software) by our talented compositing team, mixing the plate photography with the cg elements. It was common for us to allow the brightest part of the ghost to sit just behind the sternum and highlight the dark occlusive rib cage.
Step 6. Once the general composite started to work we’d fire off a pre-comp to the fx department to drive the supporting emanations. Just about all ghosts in this movie emitted an emissive vapor, a volume that surrounded the ghost. It was important to Pete Travers, the overall visual effects supervisor, for the vapor to emit as the color of the ghost on birth and transition to a more primary “ghost” color, generally green, during its lifespan. This gave the feeling that the emanations were tearing off the body’s profile, pulling the color of the ghost with it and breaking up any hard edges on the characters.
Step 7. Often volumes were not detailed enough and we’d support it by pushing millions of very small point primitives though the volume and allow them to build up in an additive way. This gave us the effect of tendrils of light and energy.
Step 8. For the all cg ghosts we also mimicked the feel of mysterious light sources over the body to tie in with the LED look. They had all the same cg layers as their hybrid counterparts.
Step 9. Generally these ghosts were flying ghosts and we added additional vapor trails in their wake. It was important for the look to keep the motion of the cloth and particles from moving too fast, as if they lived in their own viscous medium.
Step 10. We’d often reference how kelp moves underwater as a good guide for the motion and speed of our dynamic elements.
Proton Packs: Creating the Beam in 5 Steps or Less
Step 1. At Sony Imageworks we setup a system in Houdini by SideFx Software which is the go-to software package for effects animation. The fx team, lead by Pav Grochola and Joseph Cavanaugh, built a system with fx artist Filippo Maccari where a stream of single particles are fired at an intended target like an automatic weapon. Since the Ghostbusters aren’t always pointing their weapons at the right spot we’d fire the particles out of the gun barrel at the right angle and then attract those particles to the target as it moves through space.
Step 2. Connecting these particles together into a single curve gave us the general path of the beam. By using physics to drive the path we’d get nice behaviors when the Ghostbusters would move the barrel of the gun quickly, that motion would get transferred down the length of the beam over time, much like flicking the end of a rope and watching the coil move down the line. Once the general path was established we had extra controls for adding that iconic wiggle on top of the path, lots of layers of low and high frequency noise added to the base curve.
Step 3. Once the core was established we’d wrap our lightning effects around it which had a lot of control built in for artists to tweak shot by shot. Controls such as: amount of lightning paths, branching controls, distance from core, number of coils around core, thickness of lightning, etc.
Step 4. Extra lightning and energy was concentrated at the tip of the gun to give it a sense of power and we added a new element not indicated in the original movie. A molten matter dripping from the gun tip to indicate some sort of by-product burning off from the proton reaction. We based this look on bits of hot magnesium dripping from the barrel.
Step 5. For just about all of these elements we generated smoke and vapor rising off the effects. Rather than adding a simple 2D glow to our beam elements, we’d light up the smoke and vapor surrounding the beam to give us a more physical and detailed glowing look.
Creating Slimer: A 5 Step Guide
Step 1. A full maquette was built by Rick Lazzarini and used on set as a stand-in. Pete Travers had the practical character draped in green LED lights to cast interactive light into the scene and on the ghostbusters.
Step 2. For our cg version we researched the first 2 movies and found there is a lot of variety in the look of Slimer, or Onionhead as they called him, with many special purpose models sculpted for different types of actions. The production art department provided us a ZBrush model (a model sculpted in cg) as a starting place and we incorporated more features from the original movies, and from the current maquette, to arrive at the final design sculpted by our lead modeler Eric Neil.
Step 3. As part of our build our texture artist Chris Zammit sculpted extra displacement maps for wrinkles, tongue texture, and other skin imperfections in ZBrush and handled texture though Mari (a texturing program) and Photoshop. Our hair department also added peachfuzz and stray hairs for an extra level of detail.
Step 4. We added dripping slime and emanations courtesy of our fx department. Jason Williams, in look development, pulled it all together to dial the all the material properties: skin, slime, emanations, etc.
Step 5. The rigging and animation was supervised by our Animation Supervisor Sacha Kapijimpanga. We incorporated a new muscle and fat system by Ziva Dynamics (a plug-in to animation software Maya) into Slimer which added the right amount of jiggle and mass to his body.