For the 1995 "Treehouse of Horror VI" Halloween special, PDI produced over 3 1/2 minutes of computer animation for a segment entitled, Homer3. Production took about four months with a core team consisting of a director, a producer, a technical director, three character technical directors, three lighting specialists, eight character animators and nine effects animators. Because everyone at PDI was excited about the project, we opened it up to as many people as possible; at any one time, there were about 10 people dedicated to the project.
One of the joys of this project was to create a 3D environment that was a send-up of computer animation. Once Homer passes through the mystery wall into the third dimension, he encounters a landscape reminiscent of "Tron" and "The Black Hole." A pulsating green light was added to evoke an ominous feeling. The 3D set was populated with classic CG primitives (cubes, cones, cylinders), and mathematical equations hovered mysteriously in the air. Die-hard fans and the nerds among us will recognize and decipher a hexadecimal ASCII phrase, provided compliments of the Simpsons. Observant viewers will recognize the building Homer strolls past as the temple from "Myst." In one scene, a SIGGRAPH teapot appears in the background (our R&D staff did the research to determine the proper color and handle placement).
One of the most challenging aspects of this project was to create three-dimensional characters that the audience would immediately identify as the Homer and Bart they know and love. A number of surprises came out in the modeling process. We found ourselves saying, "Oh my God, Bart's hair looks like a bunch of little cones on the top of his head -- wait, Bart's hair IS a bunch a little cones on the top of his head." And, "Homer's hair is just a couple of M's glued to the sides of his head and his eyes are these HUGE spheres with 3D pupils that made them look like, well ..." We tweaked the literal interpretations to render characters that were true to their 2D appearance, but that worked in 3D.
One would think that character setup would be fairly straightforward since the characters themselves are fairly simple, but we found that simplicity to be misleading. Because the characters are smooth, clean, and "cartoony," the deformations needed to be finely honed to maintain that look. The facial system was an elaborate combination of model interpolation and custom controls, enabling our character animators to quickly rough-in lip-sync based on dialogue provided by The Simpsons in the form of exposure sheets. A series of mouth shapes were modeled to correspond to Homer's basic expressions as they appeared on the "model sheet" and were referenced by a letter on the exposure sheets. Custom controls allowed our character animators to fine-tune the expressions and create convincing performances.
Because of the large number of effects in the script, our effects team needed to be very efficient. They were told, "If it's going to take two or three weeks (to pull off a certain effect), you'll have to re-think it." The list of effects included:
The water in the pool is a good example of a simple technique that worked. A mesh of polygons was displaced by slices of a block (or slab) of three-dimensional noise. By adding just the right lighting, this simple effect gave us the look we were seeking.
Our final challenge was to bring Homer to "the scariest place yet": the real world, shot on location on Ventura Blvd. in Encino, CA. The original script called for a person in a "Homer suit." We believed our CG Homer was a better choice, and convinced The Simpsons producers to give us a shot at it.
A team from PDI attended the shoot, making sure that elements were shot in such a way that Homer could be placed convincingly into a live-action scene. We took measurements, and later simulated the actual camera and environment on the computer. Mock models of the buildings and awnings were created to assist in lighting and generating realistic shadows. We felt we needed to give Homer a different look than he had in the mysterious world of the third dimension, so we created an entirely new lighting set-up and texture maps. At one point, we tried dressing Homer in plaid pants, which looked quite funny but were too far out of character. Instead, we put him in a pair of ordinary blue jeans.
Working on Homer3 was a pleasure -- technically and creatively challenging and just plain fun. It provided an opportunity to advance our craft while poking fun at ourselves and our industry. We knew we had succeeded in creating a convincing 3D performance with a couple of iconic characters when one of The Simpsons' producers exclaimed, "You've stolen Homer's soul."