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    One Step at a Time for the Puppet of a Thousand Faces.

    CGSociety :: Production Focus
    12 February 2009, by Renee Dunlop

    Stop Motion has a new face in Henry Selick’s Coraline, a story based on the award winning book by Neil Gaiman about a little girl who finds a secret door to an “Other World” much like her own, but better… or so it seems. The first stop motion filmed in stereoscopic 3D (S-3D) during production, Selick wanted to tackle an even bigger accomplishment: creating a true stop motion film with the smooth facial transitions of CG animation in a hands-on medium.

    The answer to this quest was to use replacement animation, where one stop motion puppet face is progressively swapped for another slightly different expression with the needed smile, frown, or appropriate eyebrow position. This method is not new, but the effect is a bit choppy- often desirable for a hand made look, but has never before had all the in-betweens that Selick wanted. However, sculpting those thousands of expressions by hand would have taken years to complete. To keep the budget and timeline intact while creating stop motion animation so smooth you could read Coraline’s lips, production studio Laika creating blend shape CG face models that were output through rapid prototyping (RP).
    Compositing Coraline
    “We had an amazing group of people that came together from many different backgrounds to help make this process possible.”
    Brian McLean, Facial Structure Supervisor.
    Neil Gaiman (left), author of the book Coraline, visits director Henry Selick (right) at the LAIKA Entertainment production offices. Credit: ©2008 LAIKA, Inc. All rights reserved.
    Animator Chris Tootell readies Coraline to cross a snowy forest. Credit: ©2008 LAIKA, Inc. All rights reserved..
    Brian Van't Hul started on the project as a camera operator before assuming the title of VFX Supervisor. Coraline was his third film with Selick. Van't Hul had previously worked on James and the Giant Peach and Nightmare Before Christmas, giving him an advantage in understanding Selick’s desire. “There are a lot of technically generated perfect films out there but we thought the audience is getting used to that, and we wanted to bring back a more hand crafted look.” Van't Hul’s promotion might have been more than he bargained for. What started as one character with an interchangeable face grew into 21 characters in all requiring 15,300 different faces for the characters. The number of faces and props needed kept the three 3D Objet Geometries printers running constantly for over eighteen months.

    Laika used a hybrid of both traditional model makers and sculptures with digital artists, defining their own language along the way. Everything started with hand sculpted clay marquettes that were scanned into Maya using a 3D scanner. The faces were remodeled to maintain every detail and imperfection the original sculpt possessed; stylized wrinkles, bags under the eyes, moles and freckles that all needed to remain consistent throughout the expressions. The models were rigged using blend shapes and posed for the various facial positions, carefully noting proper placement of the tool marks from the creation process.

    The CG modelers that were hired in for the film came expecting a more or less traditional pipeline, but found they needed to retrain themselves for Coraline. Although you never see it, behind each face is an elaborate registration system and custom engineered eye mechanics. Here, instead of creating a model for digital rendering, the 3D printing was the rendering process, so new rules needed to be considered. The skin had to have thickness throughout rather than just being a digital shell. Teeth were modeled to be to be snapped in and out through the back of Coralines’ head. The interior of her mouth included the uvula, tongue, and the space under her tongue, something that would have been too time consuming if sculpted through traditional methods. Those details were in every face, even when they weren’t visible. To increase the total number of available expressions, the faces were modeled and output through RP in upper and lower halves split across the bridge of the nose, yielding 207,336 possible facial positions for Coraline, allowing for extremely subtle animation. Laika estimated to accomplish this without the CG and 3D printer process would have taken ten sculptures four years to complete. And as if that wasn’t enough. Coraline has the first stop-motion animation morphing sequence. The sequence runs for 130 frames, or nearly 6 seconds, and required 50 replacements.
    A digital camera captures the kitchen-table conversation between Coraline (at right) and her Other Father in CORALINE. Credit: ©2008 LAIKA, Inc. All rights reserved.
    The Objet RP Polyjet technology uses photopolymer resin that is housed in cartridges and sprayed down in extremely thin 16 micron layers, four times thinner than the average human hair. As it’s sprayed down in liquid form, UV lights cure each layer, hardening instantaneously. Though the process is relatively fast, a heavy model would take up too much time on the printer so each model had to have the perfect amount of detail without relying on a heavy model, detail that changed depending on the shot. Laika had to print perhaps 70 tiny half faces at a time, building what they called “kits” for various expressions, kits that had to be produced with a rapid turnover. Throughout the production the artists were continually streamlining the models to give as much detail as needed while reducing the printing time to keep up with demand. Even though the Coraline puppet was designed at less than ten inches tall allowing the sets to be smaller and conserving space, the side effect was everything was smaller. Her hands were so small they were basically the same size as the armature inside.
    Cat takes action against a duplicitous mouse in CORALINE. Credit: ©2008 LAIKA, Inc. All rights reserved.
    Other Mother's creepy true nature is revealed to Coraline. Credit: ©2008 LAIKA, Inc. All rights reserved.
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  • Rigger Oliver Jones rigs Wybie on his bicycle for a sequence in CORALINE. Credit: ©2008 LAIKA, Inc. All rights reserved.
    The CG model face halves had to meet perfectly for proper registration no matter what the expression. Any variance during printing could cause chatter once the assembled face was shot frame by frame.

    Considering the Coraline puppet was less than 10 inches tall but would be viewed on 70 foot screens, it was imperative that the seam lined up perfectly and that the hand painted textures matched. “In an example of how detailed we got,” said Brian McLean, Facial Structure Supervisor, “Coraline has little freckles, and these freckles move with her changing expressions. We had to define the depth of each freckles that could be printed out, go through the whole sanding process, priming, and layers of paint. The painters then had to hand paint these freckles and know where they had to go for each expression. Because of the precision of the models and the Objet 3D printers, we were able to dial in the exact depth of each freckle so once the faces were printed, sanded, primed and painted, all the painter had to do was drop a tiny bit of paint into the remaining hole so it would be a smooth surface. It couldn’t stick out and couldn’t sink in. The ability of the machine was so detailed that we could dial in and out exactly what we needed to accomplish this.”
    Each eyeball was an engineering feat. There is a water soluble support material that is sprayed down along side the resin, a material that washes off leaving you with a mechanically impossible piece that is locked together and movable. That material is one thing that makes the Objet printing so impressive. You are not limited to printing solid objects, you can print completely assembled ball and socket joints and working joints, creating a digital version of a working ball and socket joint that is fully assembled.

    Since the void between the ball and socket was printed with the support material, plastic mechanical joints such as the eyeball have pivot points that allow the eye to move and eyelids to blink and rotate angels. There were even movable palettes inside Coraline’s hair that allowed for her hair to bounce when she was running.
    In the Other World, Wybie (left) and Coraline (right) are drawn to a circus Credit: ©2008 LAIKA, Inc. All rights reserved.
    Other Father engineers an assist at his piano. Credit: ©2008 LAIKA, Inc. All rights reserved.
    After sanding and painting, the faces had to be testing to see how they would react to the real world lighting they would be subjected to on set, how they would tie in to the background environments, and that they retained the handmade quality that the original sculpts maintained. These pieces were under extremely hot lights, and there was initially a concern about warpage. Luckily, there was none.

    Coraline’s face was roughly one and a half to two inches across, yet when blown up to fit the widest screens there is no visible warpage.

    Even her nose, a tiny point where any unplanned movement would cause chatter by moving back and forth, was still consistent and accurate, even though the output was done on three different 3D printers that were purchased at three different times.
    Behind the scenes with Coraline (center) in the Web Living Room. Credit: ©2008 LAIKA, Inc. All rights reserved

    When the CG artists weren’t working on characters and faces, they were building props. The props luckily didn’t have to be a technically pretty computer model, the topology was not as relevant. Something like silverware or a door knob could be designed and printed in a matter of minutes, ready for sanding and painting. “We printed out growing fur for the mouse to rat morph, and replacement hair caps for the two Other Mother morphs,” said McLean. “Because these morphs had to end with the real puppet it was challenging to make sure it matched. We used ZBrush to add fur and hair detail, all while staying within the pipeline guidelines.

    “I always needed something to hold on to. I felt CG was a little sterile and I didn’t like being in front of the computer screen. But it’s neat to walk around the desks of the CG modelers here because they each have 50 or 100 pieces of models they have printed out. A lot of theses models are have pencil marks scribbled on them, highlighting subtle changes needed. It reminds us a lot of traditional drawing and sculpture process but instead of scraping away at a clay sculpt to make the changes, you dive back into the computer.”
    In the Other World, Mr. Bobinsky heralds a surprise circus attraction. Credit: ©2008 LAIKA, Inc. All rights reserved.
    Another aspect of the CG work that was needed primarily involved painting out rigs. Several of the puppets were designed in a way where they couldn’t hold their own weight, with characters large in the chest that go down to spindly legs, and require support rods sticking out the back. The animators manipulate the puppets using those rods, then those rods have to be removed in post. By shooting the animation, plus a clean plate as well, Shake and Silhouette could be used to paint out the rigs.

    Since the faces were assembled from two separate pieces, there was a visible crack between the two sections. Though the crack enhanced the handmade quality, visibly it was determined to be too distracting so the decision was made to digitally paint it out, an arduous task that needed to be handled carefully, matching the shade and value of each frame to avoid shimmer, then identically repeated for the dual frames for S-3D.
    “I was recently at an Objet user convention where traditionally it’s been about their primary focus of engineering and prototyping,” said McLean. “For the first time, there was this wave. Laika was represented there and other companies from San Francisco and Los Angeles that were just starting to use this as an artistic tool. If you look on CGSociety, you will see people posting the models that they’ve created. I think this is slowly starting to emerge and the art community is starting to embrace it. I’ve taught a lot of different people at the school and modelers at Laika, and it’s a learning curve to figure out that these have to be closed surface models, everything has to be water tight and you are constrained by real world physics. But once you embrace the rules, it’s a very exciting medium. Not only can you have a render, but you can have a nice sculpture on your desk. You can spin it around and look at it, and you will suddenly notice things you didn’t see on the computer, imperfections in the model that you wouldn’t have seen.”

    CG has gradually infiltrated every pipeline imaginable. Separated by a release date of mere weeks, CG has forever banished the Uncanny Valley through The Curious Case of Benjamin Button and now has revolutionized the stop motion art form that Ray Harryhausen pioneered. Though CG played a relatively small part in the massive effort behind Coraline, the film as is couldn’t have been done without it.
    Coraline (left) meets her new upstairs, and upside-down, neighbor Mr. Bobinsky. Credit: ©2008 LAIKA, Inc. All rights reserved.

    Related links:
    Brian McLean, Facial Structure Supervisor
    Brian Van't Hul, VFX Supervisor
    3D Equalizer
    Redlake MegaPlus II camera

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