The Advanced Art of Stop-Motion Animation: Building Puppets: Part 4
The advancement in technology using replacement faces for Coraline bridged the gap between modern computer animation and bringing the precision it offered into a physical stop-motion universe. Animator and sculptor Martin Meunier, who had worked with director Henry Selick on previous stop-motion films, served as the facial animation designer and coordinated an entire rapid prototyping department for Coraline. The process started with traditional means before going digital. Facial expression changes and lip sync were designed and animated in 2D, and then key poses were sculpted as clay maquettes and scanned into the computer. The computer animated in-between positions, and entire animated face sequences were animated in CG. Each individual frame of the computer animation was exported as an STL (stereolithography) file and printed out on an Objet 3D printer (any one of three printers installed for the production). A 3D printer is basically like a photocopy machine that prints liquid resin on a flatbed in layers. Starting from the bottom of the model it is printing, an ultraviolet light cures each layer of resin as it prints until a hard replica of the model is completed.
Once printed, each modeled piece needs to have any extra support material removed, washed, scrubbed, and sanded, and then sent to the fabrication department for painting. Each character could have as many as 15,000 faces and up to 250,000 facial expressions available, all in perfect registration to each other. The variety in expressions was created by dividing the face into upper and lower halves (Figure 3.110), so that mouth movements and lip sync could be combined with eyebrow movements in many different combinations. The seam between the two halves of the face was removed in post-production by digital effects artists. In addition to the outer appearance of each face piece, inside were details like teeth, tongues, and uvulas, as well as a complex registration system to help the pieces fit together like a puzzle. The amount of sculpting and modeling work that went into the film was estimated to be the equivalent of nearly 30 years of traditional sculpting; rapid prototyping allowed this amount to be completed in about 18 months. It allowed them to experiment with using CGI against itself by printing it out into the real world and getting artists involved in the CG process. Overall, amid all the new technical precision and subtlety offered through this technology on Coraline, the end goal was for the audience to have an emotional connection with the characters.
The Objets used on Coraline are designed to operate like a printer or photocopier, with a head that moves back and forth to print out each layer of the model. There are similar machines under different brands that employ a similar process and print a plaster-like material that also have the ability to print in color. Other machines such as EnvisionTEC printers are operated by a 250-watt bulb inside the hub of the printer (Figure 3.111), which projects the computer data from each layer onto a metal plate on the outside. The metal plate rests in a bed of liquid resin, cures each projected layer, and raises up incrementally for each layer until the model is complete and suspended upside-down (Figure 3.112). Any negative space within the model can be supported by a mesh-like support material, which is generated within the actual computer modeling software. The plate and model are removed from the printer, and support material must be cut away from the model with a hot knife (Figure 3.113) and placed in a bath for cleaning.;
The future implications for this technology to continue stop-motion productions have yet to be seen, but there could be a great deal of potential for bridging the gap between stop-motion and the capabilities of CGI. For artists who specialize in modeling or sculpting in CG using tools like Maya, ZBrush or Mudbox, printing their work in 3D can be a valuable way to transition into stop-motion if they want the experience of seeing their art in actual space. The process also has implications for easing the duplication of objects that would otherwise be cast out of molds, likewise eliminating the issue of undercuts and inconsistencies that can occur. In addition to creative applications for animation, architectural models can be realized with a great amount of detail for possible aid in creating elaborate stop-motion sets (Figure 3.114). A world of ideas and options is opened up by CG modeling’s ability to create intricate details that would be very difficult to sculpt by hand, or to physically cast in a mold. In addition, these details can be duplicated in different scales. The effect of any 3D object growing, shrinking, or morphing is possible, simply by scaling or modifying the CG model and saving each change as a separate object to be printed. Entire replacement puppets can also be animated in the computer and printed out for each frame.