Animation
Introduction
We are going to study how things move and the
creation of computer graphics representations that
look “good enough”
Rendering is: mapping light sources and surfaces to a
vector of pixel colors
Animation is: mapping objects, intentions, and external
forces to a vector of new object positions / orientations
We will not
Develop drawing skills
• but we may study how others draw so we can automate the
process
Learn how to use Maya
• but we may use Maya as a rendering tool
Hone our video game or moviemaking skills
• but we will study how modern animation technology contributes
to video games and what elements of moviemaking artistry
(timing, camera angles, etc.) must reside in animation tools
Study how things move
Who else does this?
• Biomechanists
– Physics and sensors
• Artists
– Intuition and mind’s eye
Study how things move
We’ll investigate
• Human walking, running, dancing
• Bicycle riding
• Group behaviors
• Rigid body dynamics
Generate graphics that is “good
enough”
Who else studies this?
Monet
La Cathédrale de Rouen (1894)
• Perceptual psychologists
• Artists
University of
Utah
Picasso
The Bull (1946)
Generate graphics that is “good
enough”
We’ll investigate
• Recent perceptual literature (change blindness)
• Recent computer animation experiments (faking
physics)
Completing the mapping
Bridge gap between knowledge of how
things move to how they need to be
rendered
• Artists use their minds and hands
• Computer scientists use math and programs
Traditional techniques
• Keyframing (Shoemake)
– Orientation reps (quaternion, euler)
– Curve reps (linear, quadratic, wavelets)
– Interpolation (computing arclength, Gaussian
Quadrature, SLERP)
• Disney artists (Johnson)
• Timing / storyboarding
Numerical Methods
• Curve fitting (least squares)
• Optimization
– Simulated annealing (Numerical Recipes)
– Simplex
– Spacetime Constraints (Witkin & Kass)
– Genetic Algorithms (Sims)
– Neural Networks (Grzeszczuk)
Human Motion
• Motion Capture
– Retargeting (Gleicher, J. Lee, Z. Popovic, Arikan)
– Blending (Rose)
– Abstraction (Unuma)
• Walking
– Biomechanics (McMahon, Ruina)
– Gait Generation (Metaxas, van de Panne, Hodgins)
Physical Simulation
• Rigid Body
– Physics for games (Hecker)
– Featherstone’s Method
– Constraint satisfaction
• Integration
– Runge-Kutta
– Euler
• Simplification (Chenney, Lin, Popovic)
• Perception (O’Sullivan, Proffitt)
Autonomous Agents
• Behaviors (Thalmann, Badler, Blumberg)
• Group actions (Reynolds, Brogan, Helbing)
Perception
Positive afterimage (persistence of vision)
• the visual stimulus that remains after illumination
has changed or been removed
Motion blur
• Persistence of vision causes an object to appear to
be multiple places at once
Motion Blur
Virtual camera in computer graphics
usually shoots with infinitely small
shutter speed
• No motion blur results
Without motion blur, 30 fps results in fast
moving objects that look like they are
strobing, or hopping
What’s the rate?
Playback rate
• The number of samples displayed per second
Sample rate
• The number of different images per second
Playback
Rate
Sample Rate
TV Cartoon
30
6
TV Sitcom
30
30 (on fields)
CG Lipsync
on film
24
12
Perception
Computer graphics rendering can rely on fourhundred years of perception research by artists
• The best animators have is eighty years of Disney
In 1550, after 100 years of refining the art of
perspective drawing, artists were shocked to think
that the geometric purity of their modeled world
didn’t map to recent discoveries of the human eye.
They couldn’t even imagine how cognition affected
what one “saw.” 200 more years would pass.
Animation timeline
Persistence of vision
• Thaumotrope (1800s)
• Flipbook
• Zoetrope (1834)
• Shadow puppets
pbsKids
Animation timeline
Photography
• Muybridge (1885)
• Film projector (Edison, 1891)
Animation Timeline
First Animation
• 1896, Georges Melies, moving tables
• 1900, J. Stuart Blackton, added smoke
First celebrated cartoonist
• Winsor McCay
• Little Nemo (1911)
• Gertie the Dinosaur (1914)
Animation Timeline
1910, Bray and Hurd
• Patented translucent cels (formerly celluloid was
used, but acetate is used now) used in layers for
compositing
• Patented gray-scale drawings (cool!)
• Patented using pegs for registration (alignment) of
overlays
• Patented the use of large background drawings and
panning camera
Bray’s Studio Produced
Max Fleischer – Betty Boop
Paul Terry – Terrytoons
George Stallings – Tom and Jerry
Walter Lantz – Woody Woodpecker
1915, Fleischer patented rotoscoping
• Drawing images on cells by tracing over previously recorded
live action (MoCap)
1920, color cartoons
Disney
Advanced animation more than anyone else
• First to have sound in 1928, Steamboat Willie
• First to use storyboards
• First to attempt realism
• Invented multiplane camera
Multiplane Camera
Camera is mounted above multiple planes
Each plane holds an animation cel
Each plane can translate freely on 3 axes
What is this good for?
Zooming, moving foreground characters off camera,
parallax, prolonged shutter allows blurring some layers
(motion blur)
Stop-motion Animation
Willis O’Brien – King Kong
Ray Harryhausen – Mighty Joe Young
Nick Park – Wallace and Grommit
Tim Burton – Nightmare Before Christmas
Animation Heritage
• 1963 – Ivan Sutherland’s (MIT) Sketchpad
• 1970 – Evans and Sutherland (Utah) start
computer graphics program (and Co.)
• 1972 – Ed Catmull’s (Utah) animated hand and
face (later co-founded Pixar)
• 1970’s – Norm Badler (Penn) Center for
Modeling and Simulation
and Jack
Animation Heritage
• 1970’s – New York Institute of Technology
(NYIT) produced Alvy Ray Smith (Cofounded
Pixar and Lucasfilm) and Catmull
• 1980’s – Daniel and Nadia MagnenantThalmann (Swiss Universities) become
European powerhouses
Animation Heritage
• 1980’s – z-buffer invented, SGI founded, and
Alias/Wavefront founded
• 1977 – Starwars
• 1982 – Tron (first extensive use of gfx)
• 1982 – Early use of particle systems (Star Trek
II: The Wrath of Khan)
• 1984 – The Last Starfighter (look for the Cray
X-MP in credits)
Animation Heritage
• 1986 – Young Sherlock Homes (first use of
synthetic character in film)
• 1986 – First digital wire removal (Howard the
Duck)
• 1988 – First digital blue screen extraction
(Willow)
• The Abyss (1989) Terminator II (1991) Casper
(1995), Men in Black (1997)
Animation Heritage
• ILM: Jurassic Park (1993), Jumangi (1995),
Mars Attacks (1996), Flubber (1997), Titanic
(1999)
• Angel Studios: Lawnmower Man (1992)
• PDI: Batman Returns (1995)
• Tippett Studio: Dragonheart (1996), Starship
Troopers (1997)
• Disney: Beauty and the Beast (1991), Lion
King (1994), Tarzan (1999)
• Dreamworks: Antz, Prince of Egypt
• Pixar: Toy Story, A Bug’s Life, Monster’s Inc.
Americans are hardest working
Recent history
United Nations report from Sept 1, 2003
•
$/worker-year
– US = $60,728, Belgium (top EU) = $54,333
•
hours/worker-year
– US = Japan = 1825, EU = 1300 – 1800
•
$/worker-hour
– Norway, France, Belgium, US
$38
$35
$34 $32
•
Why is US on top of $/worker-year?
– Best economies encourage widespread use of communications and
information technology
– Even though we’re fat, dumb, and happy – we don’t take month-long vacations
and one-year maternity breaks
Let’s talk about computer
animation
Must generate 30 frames per second of
animation (24 fps for film)
Issues to consider:
• Is the goal to replace or augment the artist?
– What does the artist bring to the project?
• Is the scene/plot fixed or responsive to user?
– What can we automate?
Animation – A broad Brush
Traditional Methods
• Cartoons, stop motion
Keyframing
• Digital inbetweens
Motion Capture
• What you record is what you get
Simulation
• Animate what you can model (with equations)
Computer Animation
Keyframing
Traditional animation technique
Dependent on artist to generate ‘key’
frames
Additional, ‘inbetween’ frames are drawn
automatically by computer
Keyframing
How are we going to interpolate?
From “The computer in the visual arts”, Spalter, 1999
Linear Interpolation
Simple, but discontinuous velocity
Nonlinear Interpolation
Smooth ball trajectory and continuous velocity, but loss of timing
Easing
Adjust the timing of the inbetween frames. Can be automated
by adjusting the stepsize of parameter, t.
Style or
Accuracy?
Interpolating time
captures accuracy
of velocity
Squash and stretch
replaces motion
blur stimuli and
adds life-like
intent
Traditional
Motivation
Ease-in and
ease-out is like
squash and
stretch
Can we
automate the
inbetweens for
these?
“The Illusion of Life, Disney Animation”
Thomas and Johnson
More squash and stretch
Anticipation
and Staging
Don’t surprise the
audience
Direct their
attention to what’s
important
Follow Through
Audience likes to see resolution of action
Discontinuities are unsettling
Combined
Secondary Motion
Characters should exist in a real
environment
Extra movements should not detract
Interpolation
Many parameters can be interpolated to
generate animation
Simple interpolation techniques can only
generate simple inbetweens
More complicated inbetweening will require
a more complicated model of animated
object and simulation
Interpolation
Strengths
• Animator has exacting control (Woody’s face)
Weaknesses
• Interpolation hooks must be simple and direct
– Remember the problems with Euler angle interp?
• Time consuming and skill intensive
• Difficult to reuse and adjust
Examples
Sports video games
• Madden Football
Many movie characters
• Phantom Menace
Cartoons
Motion Capture Strengths
Exactly captures the motions of the actor
• Michael Jordan’s video game character will capture
his style
Easy to capture data
Motion Capture Weaknesses
Noise, noise, noise!
Magnetic system inteference
Visual system occlusions
Mechanical system mass
Tethered (wireless is available now)
Motion Capture Weaknesses
Aligning motion data with CG character
• Limb lengths
• Idealized perfect joints
• Foot sliding
Reusing motion data
• Difficult to scale in size (must also scale in time)
• Changing one part of motion
Motion Capture Weaknesses
Blending segments
• Motion clips are short (due to range and tethers)
• Dynamic motion generation requires blending at
run time
• Difficult to manage smooth transition
Procedural
http://jet.ro/dismount
www.sodaplay.com
Examples
Inanimate video game objects
• GT Racer cars
• Soapbox about why this is so cool
Special effects
• Explosions, water, secondary motion
• Phantom Menace CG droids after they were cut in
half
Procedural Animation
Very general term for a technique that puts
more complex algorithms behind the
scenes
Technique attempts to consolidate artistic
efforts in algorithms and heuristics
Allows for optimization and physical
simulation
Procedural Animation Strengths
Animation can be generated ‘on the fly’
Dynamic response to user
Write-once, use-often
Algorithms provide accuracy and exhaustive
search that animators cannot
Procedural Animation
Weaknesses
We’re not great at boiling human skill down
to algorithms
• How do we move when juggling?
Difficult to generate
Expensive to compute
Difficult to force system to generate a
particular solution
• Bicycles will fall down
Fundamental Animation
Techniques
Fundamental Animation
Techniques
Squash and Stretch
Timing
Anticipation
Staging
Slow In and Slow Out
Arcs
Exaggeration
Secondary Action
Appeal
Personality
Squash and Stretch
More squash and stretch
Timing – is everything!
Timing
Timing = speed of action
Relays the idea behind the
action
Too fast:
• might not notice at all
• Might not understand what’s
happened
• might not pay enough attention
Too slow:
• Sense of action can be lost
• can become boring
Timing
Defines weight of the object
• Heavy objects accelerate slowly
• Size in general should correspond to the mass
Shows emotional state
Identical key frames can have different
timing
Timing example
Two key frames
• Head leaning toward the right shoulder
• Head over left shoulder, chin slightly raised
Vary the number of in-between frames, 0 to
10
Very different ideas can be communicated
Timing example, cont.
0: hit by tremendous force
1: hit by a brick, frying pan
2: nervous tick, muscle spasm
3: dodging a brick, frying pan
4: giving a crisp order “Move it !”
5: friendly “Over here. Come on - hurry”
6: sees a sports car he always wanted
7: tries to get a better look at something.
8: searches for a book on a shelf
9: appraises, considering thoughtfully
10: stretches a sore muscle
Example from: Thomas and Johnson “Disney animation –
the illusion of life”
Anticipation
Anticipation
Action has three parts
• Preparation for the action (anticipation)
• Action itself
• Termination of the action (follow through)
Need anticipation to:
• Make actions natural
– Muscle movement (kicking a ball)
• Prepare audience for the following action
• Direct attention to another part of the screen
Anticipation
Slow action: can use little
anticipation
• Meaning is carried by the
action itself
Fast action: need more
anticipation
• Need to know what’s going to
happen even before the action
Exaggerated anticipation:
• Emphasize extreme weight /
action difficulty
Staging
Follow-Thru and Overlapping
Action
Follow through
Actions rarely come to sudden stops
There are leading parts, other participating
parts and appendages
Action starts by leading part
Main action follows
Appendages continue to move longer
• Heavy ones drag along longer
Follow Through
Audience likes to see resolution of action
Discontinuities are unsettling
Overlapping action
Add variations to timing of loose parts
• Little extra actions make it more interesting
New action starts BEFORE previous one stops
• Full stops are rare
locking open door:
• Start walking to the door
• Before coming to the door, reach for the door
• Before completely closing, reach for the key, etc.
Slow in and slow out
Even spacing between
frames = constant
speed
Better to have gradual
acceleration and
slowing down
Bouncing Ball Example
The ball on the left
moves at a constant
speed with no
squash/stretch.
The ball in the center
does slow in and out
with a squash/stretch.
The ball on the right
moves at a constant
speed with
squash/stretch.
Arcs
Visual path should be an
arc
• Rather than a straight line
Exaggeration and secondary
action
Keep it balanced
Have some natural elements
and some exaggerated ones
Secondary action – results
directly from primary action
• Gives natural complexity
• Can be missed if happens in
the middle of major move
Should be obvious but kept
secondary
The secondary action of Luxo
Jr's forward motion is the
rippling of his power cord.
Exaggeration
Secondary Action
Appeal & Personality
Basic Camera Shots
Wide Shot/Establishing Shot/Long Shot
Medium Shot
Close Up Shot
Cutaway Shot/Over the Shoulder
Two Shot/Three Shot
Sequence
Length of shot
Wide Shot/Establishing
Medium Shot
Close Up Shot
Extreme Close Up
Two Shot/Three Shot
Cutaway Shot
Cutaway (CA)
cutaway is a shot that's usually of
something other than the current action.
It could be a different subject (eg. this
cat when the main subject is its owner),
a close up of a different part of the
subject (eg. the subject's hands), or just
about anything else.
The cutaway is used as a "buffer"
between shots (to help the editing
process), or to add interest/information.
A
Basic Camera Moves
Zoom In
Zoom Out
Pan Right, Pan Left
Action in the frame.
Follow the action/rolling shot.
Standard Movie Openings
Movie Opening 1
Movie Opening 2
Wide Shot
Tight Close-Up
Zoom to Medium
Out to Medium
Some Action.
Action
Zoom to close-up
Zoom to close-up
Out to Medium.
Out to Medium
Most Bond Films
Run with it.
Raiders of Lost Ark