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Computer Graphics
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Computer Animation
December 07, 2005
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Computer Animation
“Animation”making objects change over time according to scripted
actions
“Simulation”predicting how objects change over time according to
physical laws
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Contents
Principles of animation
Keyframe animation
Articulated figures
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Principle of Traditional Animation – Disney –
Squash and stretchSlow in and outAnticipationExaggerationFollow
through and overlapping actionTimingStagingStraight ahead action
and pose-to-pose actionArcsSecondary actionAppeal
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Squash and Stretch
Squash
Stretch
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Slow In and Out
Slow
Slow
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Anticipation
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Animation Pipeline
3D modeling
Motion specification
Motion simulation
Shading, lighting, & rendering
Post-processing
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Contents
Principles of animation
Keyframe animation
Articulated figures
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Keyframe Animation (1)
Defining character poses at specific time steps called
“keyframes”
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Keyframe Animation (2)
Interpolating variables describing keyframes to determine poses
for character “in-between”
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Inbetweening (1)
Linear interpolationusually not enough continuity
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Inbetweening (2)
Spline interpolationmaybe good enough
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Inbetweening (3)
Spline interpolationmaybe good enoughmay not follow physical
laws
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Inbetweening (3)
Spline interpolationmaybe good enoughmay not follow physical
laws
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Inbetweening (4)
Inverse kinematics or dynamics physical laws
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Contents
Principles of animation
Keyframe animation
Articulated figures
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Articulated Figures (1)
Character poses described by the set of rigid bodies connected
by “joints”
Base
Arm
Hand
Scene Graph
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Articulated Figures (2)
Well-suited for humanoid characters
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Articulated Figures (3)
Inbetweeningcomputing joint angles between keyframesconsidering
the length constancy
Right Wrong
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Example: Walk Cycle (1)
Articulated figure:
Hip
Knee
Foot
Upper Leg
Ankle
Lower Leg
Hip Rotate
Hip Rotate + Knee Rotate
Upper Leg (Hip Rotate)
Foot (Ankle Rotate)
Lower Leg (Knee Rotate)
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Example: Walk Cycle (2)
Hip joint orientation:
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Example: Walk Cycle (3)
Knee joint orientation:
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Example: Walk Cycle (4)
Ankle joint orientation:
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Challenge of Animation
Temporal aliasingmotion blur
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Temporal Ailasing
Artifacts due to limited temporal
resolutionstrobingflickering
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Temporal Ailasing
Artifacts due to limited temporal
resolutionstrobingflickering
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Temporal Ailasing
Artifacts due to limited temporal
resolutionstrobingflickering
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Temporal Ailasing
Artifacts due to limited temporal
resolutionstrobingflickering
Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Motion Blur
Compositing weighted images of adjacent frames
removing parts of signal under-sampled in time
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Sun-Jeong Kim http://www.hallym.ac.kr/~sunkim/teach/2005/cga
Summary
Animation requires ...modelingscriptinginbetweeninglighting and
shadingrenderingimage processing
