17-animation

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					                                                             Computer Animation
                                                             • What is animation?
                                                                 ! Make objects change over time
                                                                   according to scripted actions

         Computer Animation
                                                                                                                Pixar
                                                             • What is simulation?
                                                                 ! Predict how objects change over time
                 Adam Finkelstein                                  according to physical laws
                Princeton University
               COS 426, Spring 2005


                                                                                                          University of Illinois




Outline                                                      Principles of Traditional Animation
• Principles of animation                                    •   Squash and stretch
• Articulated figures                                        •   Slow In and out
                                                             •   Anticipation
• Keyframe animation                                         •   Exaggeration
                                                             •   Follow through and overlapping action
                                                             •   Timing
                                                             •   Staging
                                                             •   Straight ahead action and pose-to-pose action
                                                             •   Arcs
                                                             •   Secondary action
                                                             •   Appeal
                                             Angel Plate 1                                                                   Disney




Principles of Traditional Animation                          Principles of Traditional Animation
•   Squash and stretch                                       • Squash and stretch
•   Slow In and out
•   Anticipation
•   Exaggeration
•   Follow through and overlapping action
•   Timing
•   Staging
•   Straight ahead action and pose-to-pose action
•   Arcs
•   Secondary action
•   Appeal
                                                  Disney                                                                Lasseter `87
Principles of Traditional Animation                      Principles of Traditional Animation
•   Squash and stretch                                   • Slow In and Out
•   Slow In and out
•   Anticipation
•   Exaggeration
•   Follow through and overlapping action
•   Timing
•   Staging
•   Straight ahead action and pose-to-pose action
•   Arcs
•   Secondary action
•   Appeal
                                                Disney                                           Watt Figure 13.5




Principles of Traditional Animation                      Principles of Traditional Animation
•   Squash and stretch                                   • Anticipation (and squash & stretch)
•   Slow In and out
•   Anticipation
•   Exaggeration
•   Follow through and overlapping action
•   Timing
•   Staging
•   Straight ahead action and pose-to-pose action
•   Arcs
•   Secondary action
•   Appeal
                                                Disney                                              Lasseter `87




Principles of Traditional Animation                      Example: Roadrunner
•   Squash and stretch
•   Slow In and out
•   Anticipation
•   Exaggeration
•   Follow through and overlapping action
•   Timing
•   Staging
•   Straight ahead action and pose-to-pose action
•   Arcs
•   Secondary action
•   Appeal
                                                Disney                                           Warner Brothers
Computer Animation                                                Example: Luxo Jr.
• Animation pipeline
   !   3D modeling
   !   Motion specification
   !   Motion simulation
   !   Shading, lighting, & rendering
   !   Postprocessing




                                                        Pixar                                                                    Pixar




Outline                                                           Articulated Figures
• Principles of animation                                         • Character poses described by set of rigid bodies
                                                                    connected by “joints”
• Articulated figures
• Keyframe animation                                                      Base


                                                                          Arm


                                                                         Hand

                                                                      Scene Graph

                                                 Angel Plate 1                                                  Angel Figures 8.8 & 8.9




Articulated Figures                                               Articulated Figures
• Well-suited for humanoid characters                             • Joints provide handles for moving
                                                                    articulated figure
                   Root

           Chest              LHip      RHip

 Neck     LCollar LCollar    LKnee      RKnee

 Head      LShld    LShld    LAnkle RAnkle

          LElbow LElbow

          LWrist    LWrist
                                                Rose et al. `96                         Mike Marr, COS 426, Princeton University, 1995
Example: Robot                                                              Articulated Figures
                                                                            • Inbetweening
                                                                              ! Compute joint angles between keyframes




                    Mihai Parparita, COS 426, Princeton University, 2003                                                       Watt & Watt




Outline                                                                     Keyframe Animation
• Principles of animation                                                   • Define character poses at specific time steps
                                                                              called “keyframes”
• Articulated figures
• Keyframe animation




                                                            Angel Plate 1                                                      Lasseter `87




Keyframe Animation                                                          Keyframe Animation
• Interpolate variables describing keyframes to                             • Inbetweening:
  determine poses for character in between                                    ! Linear interpolation - usually not enough continuity




                                                                                          Linear interpolation




                                                            Lasseter `87                                                   H&B Figure 16.16
Keyframe Animation                                                 Keyframe Animation
• Inbetweening:                                                    • Inbetweening:
   ! Spline interpolation - maybe good enough                         ! Cubic spline interpolation - maybe good enough
                                                                         » May not follow physical laws




                                                H&B Figure 16.11                                                    Lasseter `87




Keyframe Animation                                                 Keyframe Animation
• Inbetweening:                                                    • Inbetweening:
   ! Cubic spline interpolation - maybe good enough                   ! Inverse kinematics or dynamics
      » May not follow physical laws




                                                    Lasseter `87                                                    Rose et al. `96




Example: Walk Cycle                                                Example: Walk Cycle
• Articulated figure:                                              • Hip joint orientation:




                                                    Watt & Watt                                                     Watt & Watt
Example: Walk Cycle                                            Example: Walk Cycle
• Knee joint orientation:                                      • Ankle joint orientation:




                                                 Watt & Watt                                                Watt & Watt




Example: Red’s Dream                                           Challenges of Animation
                                                               • Temporal aliasing
                                                                  ! Motion blur




                                                 (Pixar)




Temporal Aliasing                                              Temporal Aliasing
• Artifacts due to limited temporal resolution                 • Artifacts due to limited temporal resolution
   ! Strobing                                                     ! Strobing
   ! Flickering                                                   ! Flickering
Temporal Aliasing                                                           Temporal Aliasing
• Artifacts due to limited temporal resolution                              • Artifacts due to limited temporal resolution
   ! Strobing                                                                  ! Strobing
   ! Flickering                                                                ! Flickering




Motion Blur                                                                 Summary
• Composite weighted images of adjacent frames                              • Animation requires ...
   ! Remove parts of signal under-sampled in time                              !   Modeling
                                                                               !   Scripting
                                                                               !   Inbetweening
                                                                               !   Lighting, shading
                                                                               !   Rendering
                                                                               !   Image processing




                                                                                                                                                Pixar




Example: Robot                                                              Example: Ice Skating




                                                                                                       (Mao Chen, Zaijin Guan, Zhiyan Liu, Xiaohu Qie,
                     Mihai Parparita, COS 426, Princeton University, 2003
                                                                                                            CS426, Fall98, Princeton University)

				
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