Motion for Computer Animation Michael Gleicher Department of Computer Sciences University of Wisconsin, Madison
Motion for Computer Animation
Michael GleicherDepartment of Computer
SciencesUniversity of Wisconsin,
Madison
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Outline
n A brief history of computer animationn (animation appreciation) – Video!
n Techniques for creating motionn (an overview) – Video!
nMotion retargetting and spacetimen (what I do) – Video!
n Graphics and Animation at UW CS
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Goals
n Give you some idea of what Computer Animation is about
n Give you some idea of where (some of) the hard problems are
n Give you an idea of what I don Show some fun video
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Caveats
n This talk is skewed toward 3D Animation for film and video
n That ignores lots of interesting stuffn 2D and image effectsnGames, Visualization, Simulation, ...
n Focus on character animationnOver-emphasize my heroes
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Timeline
n Phases of the history of animation
PioneersPioneersComing
Of Age
ComingOf Age
1982 1987
EarlyDays
EarlyDays
ModernEra
ModernEra
1997
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Pioneer Days (pre-1980s)
n What was happening:n Early pioneers (in research labs) started
making movies with computersn General Story:n It was hard to make pictures with computers,
but people did it anywayn Why it ended:n Computer Animation becomes feasible
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Early Days (early to mid-1980s)
nWhat was happening:nComputer animation in film and video
nWhat it looked like:nComputer graphicsn Things computers could draw wellnChrome! Flying Logos!
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Early Days (early to mid-1980s)
n Notable examples:n TRON (‘82), The Last Starfighter (’84)nMany TV spots and commercials
nWhat it looks like today:nQuaint
nWhy it endedn AUDIENCES grew more savvy
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
A critical moment in history…
n First computer animation nominated for an Academy Award
n Notable character animationIt’s the motion! (well, it looks good too)
Luxo Jr.Pixar, 1986J. Lasseter (dir)
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Computer Animation Comes of Age(late 80s – mid 90s)
n Computer Animation not just for computer animation’s sake
Beauty and the Beast, 1991 Jurassic Park, 1993
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Glory Days of Computer Animation
nWhat will they do next?n Notable examplesn Tin Toy ’88 (and other Pixar Shorts)n Terminator 2 ’91n Beauty and the Beast ’91n Jurrassic Park ’93n… more and more and more …
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Another important film…
n Feature length, 3D animated filmn Financially and artistically successfuln Everybody wants to copy
Toy StoryPixar, 1995J. Lasseter (dir)
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Why is Toy Story Different?
n Same basic technology as shortsn Different magnitude of problemsnHow to deal with all the bits!
nMust hold attention for 90 minutes
Tin Toy1988
Toy Story1995
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
End of the Glory Days?
n Glory is for good films, not cool effectsnNot just animation for animation’s sakenHackers are not the heroes anymore
n Technology is generally available.n (Kindof)
n Artistic factors drive
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Toy Story++
nMore and more animated filmsn Greater levels of complexityn Antz, Bugs Life, Toy Story 2, …
n New artistic styles and possibilitiesn Tarzan, Prince of Egypt, …
n Current state of the art
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
The Post-Modern Era (’97- …)
n Don’t believe your eyes!n Anything is possible!n Seamless integration of CG and real
n Some landmarksn Titanic ’97nWhat Dreams May Come ‘98n The Mummy, Phantom Menace ‘99
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
How do you do it?
n “Typical” or Traditional pipelinen Divides tasksn Variants exist
Design Modeling Animation Lighting Rendering Post-Production
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Design
n One of the most important piecesn Deciding what animation is to be
made
Design Modeling Animation Lighting Rendering Post-Production
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Modeling
nWhat are the objects?nWhat do they look like?
Design Modeling Animation Lighting Rendering Post-Production
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Animation
n Animate: to bring to lifenMaking things move
Design Modeling Animation Lighting Rendering Post-Production
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Lighting
nMaking choices in how things lookn Term is a “Pixarism”
n Catch-all for lots of appearance design
Design Modeling Animation Lighting Rendering Post-Production
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Rendering
n Let the computers color the pixels
Design Modeling Animation Lighting Rendering Post-Production
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Post-Production
n Put the pictures into final form
Design Modeling Animation Lighting Rendering Post-Production
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Why focus on motion?
n It is the heart of animationn It’s the most unique aspect of
animationn It’s the thing we have the least
experience withn It’s the thing I am most interested in
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
What is a motion?
(x,y)θ
θ
θ
p = {x,y,θ1,θ2,θ3,...}
θ θ
θ
θ
n Animated Charactern Pose or Configuration
n parameters in a vector
n Examples are articulated figures (humans)n trees of rigid linksn center + joint anglesn nothing specific about methods
p ∈ℜn
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
What is a motion (2)
n A motion maps times to configurations
n Vector-valued, time-varying signal
n Representation comes from creationn typically interpolationn may not be convenient for
editing Time (t)sig
nal
(p
)
m(t) ∈ℜ ⇒ ℜn
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Three main ways to make motion
n Create it by handn Compute itn Capture it from a performer
n Re-use an existing motionn (don’t make it at all)
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Creating Motion by Hand:Keyframing
n Skilled animators place “key” posesnComputer “in-betweens”
n Requires incredible amounts of talentn But can be done extremely well
Verdict: Produces the highest quality results, at a very high cost
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Computing Motion:Procedural and Simulation
n Define algorithms to create motionsn Ad-hoc rules, or simulate physicsn Physics provides realismn But how do you control it?
Verdict: Good for secondary effects, not for characters (yet)
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Motion Capture and Performance Animation
n Use sensors to record a real personn Get high-degree of realismnWhich may not be what you want...
n Possibility for real-time performance
Verdict: Good for realistic human motions. Scary to animators.
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Motion Capture Technology:Optical Tracking
n User markers and special camerasn Tracking + Math
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Motion Capture Technology:Video
n An interesting and open problem…n Limited informationn But seemingly enough
n Problem can be arbitrarily hardnOr easy – if you make assumptions
n Video is surprisingly bad
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
So now you have motion...
n Transform Motion to new uses
Problem: Motion is Specific
Specific ActionSpecific Action Specific CharacterSpecific Character
hand isnot herehand isnot here
different sizedcharacterdoesn’t fit
different sizedcharacterdoesn’t fit
Edit motion to meet new needsEdit motion to meet new needs
Retarget motion to new characterRetarget motion to new character
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Retargetting Motion to New Characters
n Goal: one motion, a cast of characters
n Focus on similar structure
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Transformation BasicsChange what isn’t important, retain what is
n Hard to define what is importantn high-level propertiesnmotion specific
n Stick to what’s easy to definen geometric constraintsn signal characteristicsn framework for better metrics later
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Transformation as Constrained Optimization
n Find a motion that…1. Meets any specific requests2. Keeps any specific characteristics of the
original3. Is as similar as possible to the original
n Naturally posed as constrained optimizationn subject to meeting the constraints (1 and 2)
minimize some objective (3)
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Spacetime Constraints
n Consider all constraints simultaneouslyn NOT frame at a time
n Solve for motionsn “best” motion that meets constraints
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
What makes a jump a jump?
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
What makes a jump a jump?
BalanceBalanceElbow doesn’t bend backwardsElbow doesn’t bend backwards
Arms swingArms swing Knees bendKnees bend
No skiddingNo skiddingF=MAF=MAFeet start on floorFeet start on floor
Geometric Constraints - implement as constraintsSignal Characteristics - get from signal matchingOther Constraints - could be added later
Geometric Constraints - implement as constraintsSignal Characteristics - get from signal matchingOther Constraints - could be added later
Feet end up on floorFeet end up on floor
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Basic Idea 1: Constraints
Exact parameter values may not be important
Geometric constraints often are important
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Basic Idea 2: Frequency Content
n High frequencies (abrupt changes) are significant and noticeable
n Altering high-frequencies changes motions
n Adaptations should avoid disturbing high frequencies
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Retargetting Recipe
1. Define Constraints
2. Apply to new character
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Retargetting Recipe
3. Approximate Answer
4. Solve constraints (band-limited adaptation)
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Retargetting Results
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Some successesOriginalMotion
Adapt FemaleOnly Adapt Both
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Characters with Different Structure
n Creativity vs. Automationn User defines point
correspondencesn Adapt similar structure to same
size firstn Different numbers of degrees of
freedomn least squares (too few)n objective (too many)
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
What does it take to do this?
n Setup and Solve a BIG math problemnNon-linear, variational, constrained
optimization
n Thousands of simultaneous equationsn Yes, you can do it in real timenwith some caveats...
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
How did we do that?
Get Motion(from library)
AnnotateConstraints
Get Character(from library)
Devise skeletonfor character
ComputeAdapted Motion
Lighting Render
ConvertSkelleton
Get from library(stock CD or Web)
Our Software
Commercial Animation System(3D Studio MAX)
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
Graphics at UW CS
n Target for growth in the departmentn New courses:n Introduction to Graphics
n now taught as CS638, will get new number soon
nComputer Animationn now taught as CS838, will get new number soon
nOther courses elsewheren Art (comp. anim), ECE (image proc), ...
October 26, 1999Motion for Computer Animation
© 1999, Michael L Gleicher
To Learn More...
n Take Graphics and/or Animationn Look on the webnHodgin’s motion overview in Scientific
Americann “Why Files” introductory articlen A lot of stuff is on the 838 Web from last
year (access from my home page)