Sophisticating Shrek 2

Sophisticating Shrek 2
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By Larry Cutler and Lucia Modesto
May 1, 2004 12:00 PM
An inside look from PDI/DreamWorks
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About 2 1/2 years ago, the character technical director
(TD) department at PDI/DreamWorks, Redwood City,
Calif., started developing characters for the animated
feature Shrek 2. Since the release of the original Shrek film in 2001, we
had implemented a number of new techniques for setting up characters,
and our team was eager to tackle the many challenges posed by the initial
Shrek 2 script. Our lofty goal was to create characters that would run
faster, capture more complexity, and look even better than the original
Shrek's animated cast.
On any computer-generated feature,
the character TD group is responsible
for setting up the characters for
animation and is one of the first
departments to begin working on the
film. At this early phase of the
project, the story and art
departments are just beginning to
define the movie. It is an interesting
time for the artists involved, because
character TDs participate directly in
the character design process —
initially finding out from the directors
the types of actions that a character
has to perform, its range of motion,
the number of outfits, and any other
behaviors specific to the character.
This process is very collaborative as
character TDs give input on how to
modify the character design to best
achieve all the performance
PDI visual effects supervisor Ken
requirements.
Bielenberg works to tweak the
character Prince Charming, one of
Blending Old and New
several new human characters that
required a more sophisticated
approach in Shrek 2, particularly
The challenge given to us for Shrek 2
regarding cloth and hair issues.
by directors Andrew Adamson, Kelly
Photos courtesy of DreamWorks,
Asbury, and Conrad Vernon, as well
TM & © DreamWorks, LLC. All
as visual effects supervisor Ken
Rights Reserved.
Bielenberg, was to create a movie “at
least 10 times more sophisticated than the original.”
Indeed, the script for Shrek 2 had many new human main characters as
compared to the first film, including Prince Charming (voiced by Rupert
Everett), the Fairy Godmother (voiced by Jennifer Saunders), the King and
Queen (voiced by John Cleese and Julie Andrews), among others. Most
characters had a number of different outfits, including armor and elaborate
hairstyles. In addition, the story also introduced new sidekick
Puss-in-Boots (voiced by Antonio Banderas), a complicated cat covered in
fur with many moving accessories like a sword, belt, and hat. Once the
character design is approved, the modeling department creates a 3D model
of the character and the character setup process begins. The setup has
many distinct parts, which together transform the neutral model into a
fully articulated, deforming character.
First, a motion system is built by adding joints that represent the skeletal
structure of the character's body and face. The setup exposes hundreds of
animation controls, which allow an animator to move and rotate the
individual joints. The next step is attaching the model to these joints,
using various deformation techniques that will mimic the results of real
bones and muscle effects on skin. For the human characters, the setup
also includes a hair motion system and a clothing deformation system.
In order to accommodate the story and the more sophisticated look for
Shrek 2, our Academy Award-winning character TD guru, Dick Walsh (see
“Hackers' Ball,” March 2003 for more on the Technical Achievement Award
he won for his groundbreaking work on the PDI Facial Animation System),
further augmented our facial setups with subtle details such as
anatomically correct neck muscles, an Adam's apple, crow's feet wrinkles,
and bulging jaw muscles. Walsh and character TD Luca Prasso revamped
our character body deformations with the same proprietary technology that
drives our facial system. This solution provided a better range of
deformations, simplified our setups, and made the characters run faster for
animation.
A new “fitting” method was also
developed to transfer the basic
deformations from one character to
another. Fitting works by first
another. Fitting works by first
delineating a set of key features that
define the body and face. The
algorithm then warps the deformation
system to the new character based
on these features. This technique
significantly reduced the character TD
setup time, allowing us to
successfully deliver more human
characters than on the original Shrek.
A challenge unique to
computer-animated sequels is how
best to maintain the “legacy”
characters from the first movie, such
as lead characters Shrek, Donkey,
and Fiona. Several years had passed
from the creation of these original
setups to the beginning of work on
Shrek 2. During that period, nearly
every aspect of our animation
environment had changed. The
underlying animation software had
become more sophisticated; a new
feature film pipeline made it easier to
exchange data between department
Top: Queen Lillian and King
assets; and our character
Harold. Center: Larry Cutler, one
deformation technologies had evolved
of the character TD supervisors
in new directions.
who is part of the team that
Therefore, at the beginning of Shrek improved PDI's approach for
setting up and animating human
2, our legacy characters had to be
characters in Shrek 2. Bottom:
upgraded to integrate numerous
character setup improvements, while Prince Charming and Fairy
Godmother.
still maintaining the integrity of the
established look from the first movie. During production, the legacy setups
often needed additional upgrades based on new story requirements, such
as exposing bare feet and toes and adding new outfits. For some
secondary characters, however, it was more cost-effective to build new
setups, rather than dealing with the complexity of making significant
enhancements.
Realistic Crowds
Digital technologies have enabled filmmakers to employ more complex
visual palettes to tell their stories with a greater scope of imagination. In
films such as The Lord of the Rings trilogy, entire scenes revolve around
the convincing actions performed by thousands of computer-generated
background characters. These demands have driven the special effects and
computer animation industries to develop increasingly complex crowd
systems capable of generating a wide range of digital extras that can
perform sophisticated actions in a scene.
Not surprisingly, the Shrek 2 story required a larger and more varied cast
of secondary characters and digital extras. Guillaume Aretos, our
production designer, and visual effects supervisor Ken Bielenberg also
wanted to substantially heighten the level of visual richness and depth of
animation in these background characters. This necessitated a concerted
preproduction effort to improve the modeling, character setup, animation,
surfacing, and lighting on secondary characters.
Since it would be impossible to provide individual setups for each
background character, our approach was instead to build six archetype
generic humans: two adult men, two adult women, and two children.
Different physique, facial, and wardrobe variations were added on top of
the default generics to deliver a wide spectrum of possible characters.
We designed a new generic character pipeline for Shrek 2 to make the
setup process easier and to produce a broader range of variation in
comparison to Shrek. This process provided for a more art-directed look,
yet did not require hand-tweaking the character deformations for individual
variations. Since generics are often cast in various roles, the setups were
built with the exact same set of animation controls and deformations as
the main characters. This helped our animation and lighting departments
keep a visual consistency between the hero characters and the secondary
characters.
When casting a secondary character in the movie, Aretos could choose one
of five physiques, one of the available face variations (they vary from five
to 15 possible faces), an outfit (on average, seven per generic character),
a hat (about 15), a hairstyle (about five), and props such as earrings,
rings, necklaces, etc.
Having these generic character
setups made it easier to change
outfits, physiques, or faces of
secondary characters without
requiring additional character setup
work. Occasionally, the story required
a very specific face shape, such as
with Captain Hook or Joan Rivers. In
these cases, our regular face
variation technology could not quite
achieve the desired look. Instead of
creating a new setup, character TD
Dug Stanat developed a technique for
adding an additional layer of
deformations on top of the facial
system to sculpt that extra detail.
On the original Shrek, effects
On the original Shrek, effects
animators used a proprietary crowd
simulator called Mob to procedurally
animate the hundreds to thousands of
secondary generics required for
specific shots. First, a library of
character models was created for
every type of action needed on a
sequence. Then, the crowd system
distributed these models in the scene.
However, this system primarily
positioned and interpolated the
Top: The film's star, Shrek.
models and could not easily support
Center: Lucia Modesto, character
more complex interactions with the
TD supervisor. Bottom:
shot environment.
Puss-in-Boots and Donkey, two key
animal characters in the film.
For Shrek 2, character TDs Shawn
Lewis and Gilbert Davoud teamed up Puss-in-Boots was a complicated
with FX developer Jonathan Gibbs to character because of his fur and
moving accessories such as his
create a new approach. Dubbed
hat, sword, and boots.
“Dynamic Crowd Control” (DCC), it
enabled crowds to be run in the shot with complete character deformations
computed at every frame.
This new system allowed the characters to better interface with the shot
environment — for example, by enforcing their feet to lock properly when
walking on a sloped terrain, and their bodies to stay balanced. High-level
behaviors such as head turns, eye tracking, and hand/arm adjustments
could be applied on top of an action to allow for additional interactions
with the scene. Finally, the software could blend multiple cycles together.
This feature was used to transition between two different actions, or to
layer one action on top of another.
The DCC system gave the effects animator more control over the
characters' movement in a shot, but took longer to compute since the
characters' final deformations are calculated at every frame. Thus, a
combination of both techniques was used in production crowd shots, with
the number of dynamic crowd characters varying from none to more than
a hundred.
Fashion Statements
Shrek 2's story and art necessitated improvements to the character TD
clothing pipeline, as well. Shrek 2 has a wide variety of human characters,
each with multiple costume changes during the film. Many of these outfits
were significantly more elaborate than what we had done successfully for
Shrek.
Our studio has typically taken a dual approach with clothing. The clothing
department usually runs physically based dynamic simulations to generate
looser garments that automatically react to the motion of the character. In
contrast, our TD department handles tighter outfits as part of the
character setup without using a simulation. The challenge with
non-simulated cloth is to fake a few of its key properties, such as sliding
on top of the skin, adhering to gravity, and blending in wrinkles.
Perhaps the most important visual cue for cloth is its unique folds and
wrinkle patterns. To help apply this behavior in our character setups,
Erwan Maigret and Reid Gershbein, members of the R&D staff, developed
a system to paint realistic wrinkles onto clothing. The wrinkles change
throughout an animation based on the local compression of points on the
clothing surfaces. The results mimic the physical behavior of cloth, but do
not require running a dynamic simulation. For each outfit, a character TD
generates various sets of wrinkled poses. During an animated sequence,
the system uses these wrinkle poses to simulate the shape of a wrinkle on
cloth.
Shrek 2 also had a number of more complicated outfits that required a
hybrid solution involving tighter integration between character setup and
dynamic clothing. For example, the Queen, Fairy Godmother, and Fiona all
wear one-piece flowing gowns that drape to the floor during a formal ball
sequence. For these outfits, the final geometry was assembled by a blend
between an upper portion deformed by the character TD setup and a lower
section simulated by the clothing department.
Generating realistic looking, yet
controllable, hair motion was another
challenge made more difficult by the
number of human characters
appearing in Shrek 2. To tackle this
problem, character TD Nico Scapel
developed a new “wig” system for us.
This system gave animators manual
control over the hair, and then
layered a physically based simulation
on top of the animated motion. The
system provided a number of
high-level controllers that animators
moved around to affect different
regions of the hair. They could also
pose key features, such as bangs or
braids.
The high-level controllers drive a dynamic simulation that is applied to
each individual hair. On-demand gravity allows a character's hairstyle to
be modeled with gravity built-in, and still respond realistically to head
motion. Collision is handled by the system for specific hair situations, such
as the King's hair colliding against his crown.
During production, the “wig” system provided a nice blend between
automatic simulation and hand-animated control. When necessary,
automatic simulation and hand-animated control. When necessary,
animators could tweak the dynamics or exaggerate the hair motion based
on director comments. However, in most cases no animator involvement
was necessary.
In all, these many new character setup developments combined to
produce a higher visual complexity and subtle extra details on the
characters. We hope that all this effort, together with the performances
created by the animators, the special effects generated by the effects
department, and the rendered final look from our surfacing and lighting
departments, helped to achieve the goals of bringing a more sophisticated
world to life in Shrek 2.
Larry Cutler and Lucia Modesto currently serve as character TD
supervisors at PDI/DreamWorks, and at press time were finishing work on
Shrek 2.
With PDI/DreamWorks since 2001, Larry Cutler previously worked at Pixar
Animation Studios as a technical director on such films as Monsters, Inc.,
Toy Story 2, and A Bug's Life. Prior to that, he worked in the Stanford
Computer Science Department both in research and teaching, after serving
internships at both Silicon Graphics and the Microsoft Corporation.
Cutler also served as the co-founder and president of Hyperjive, Inc., a
startup company developing mobile information-sharing applications. He
attended Stanford University and graduated with both a bachelor's and
master's in computer science.
With PDI/DreamWorks since 1997, Lucia Modesto also served as a
co-character technical director/supervisor for the Academy Award-winning
original, Shrek. Specializing in character setup, Modesto is responsible for
setting up the joints, animation controls, and facial animation, as well as
writing the software to make characters move and change smoothly.
Joining PDI/DreamWorks in 1997 to work on the company's first computer
animated feature, Antz, Modesto was already familiar with the studio's
technology. She spent almost two years in the early 1980s working at
PDI/DreamWorks on some of the first animation projects for TV Globo.
A native of Rio de Janeiro, Brazil, Modesto was educated as an electronic
engineer at the Federal University of Rio de Janeiro. She later received a
master's degree in quantum electronics and applied optics at UCLA.
Modesto also served as an intern at the National Film Board of Canada on
a scholarship jointly granted by Canada and Embrafilme.
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