Outline
Animation 1 Animation COM3404 2 Key-framing 3 Skeletal animation Richard Everson 4 Motion Capture School of Engineering, Computer Science and Mathematics University of Exeter References [email protected] http://www.secamlocal.ex.ac.uk/studyres/COM304 Fundamentals of 3D Computer Graphics. Watt. Computer Graphics: Principles and Practice. Foley et al (1995). Principles of Three-Dimensional Computer Animation. M. O’Rourke.
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Animation Victorian animation
Animation Bring to life Phenakistoscope Zoetrope
Moving graphics of any kind: sequences of single images flipbooks, kineographs phenakistoscope, zoetrope cartoon films computer animation Speed 6 frames per second for impression of movement Films: 24 fps TV: 30 fps Computers: upto 100 fps Double buffering Render to off-screen buffer; swap with displayed buffer
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Specify positions in a few key frames
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Objects Size, position, rotation, colour, texture, shape 40602
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Key frame interpolation Example: Blender
Linear interpolation A fighter dives into a canyon, flies next to the water and rises again. The t − t0 camera follows the motion and there is a reflection in the water. v(t) = v0 + (v1 − v0) t1 − t0 t − t0 x = x0 + (x1 − x0) t1 − t0 t − t0 y = y0 + (y1 − y0) t1 − t0 t − t0 z = z0 + (z1 − z0) t1 − t0 Simple Motion appears jerky at the key-frames Spline interpolation Hermite splines or NURBS give fine control over location Hermite splines guaranteed to pass through control points Most modelling packages allow interactive editing of motion path Linking of paths to permit camera to track a moving object etc.
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Key 1 2 3 4
Key 5 6 7 8
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Keyframing: collision avoidance Keyframing
Keyframing of limbs requires a significant additional effort to avoid collions and unrealistic positions during interpolation. Inverse kinematics determines joint motions necessary to achieve a goal: more in following lectures. Key 9 10 11 12 Additional constraints to limit the joint only to realistic motions. Lotus position keyframing by Jean-Christophe Nebel, Keyframe interpolation with self-collision avoidance in Computer Animation and Simulation ’99, pages 77-86. Eurographics, 1999.
Key 13 14 15 16
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Choose rotation axis Interpolate angle about axis Interpolation can be done in Interpolate takes the shortest path on a unit sphere (geodesic path) RGB or HSV space
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Skeletal animation: rigging Matrix palette skinning
Animating complex polygonal meshes Bones of skeleton each has a transformation matrix Mi describing its animation from the 0 X Construct a skeleton of untransformed location in world v = wi Mi v bones capturing the coordinates i components and joints of Vertices are a linear combination the body v untransformed vertex (blend) of a palette of neighbouring location Rig the skeleton by bone locations: 0 attaching vertices to v transformed vertex skeleton location Animate skeleton Mi transformation matrix v describing motion of Each vertex location is a w1 bone i weighted combination of w2 wi weighting for ith bone. bone locations: P eg: 1 part shin and 2 parts i wi = 1 thigh for a vertex in the knee
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Untransformed bones and mesh Texture mapped mesh http://www.gup.uni-linz.ac.at/∼gk/Praktika/meshskin webdata/ Transformed bones and mesh Texture mapped mesh http://www.gup.uni-linz.ac.at/∼gk/Praktika/meshskin webdata/ Richard Everson Animation 37 / 43 Richard Everson Animation 38 / 43
Morph target animation Morph target animation
Vertices of key-frames are edited manually Intermediate frames interpolated
Artist has more fine control over location Libraries of facial expressions corresponding to emotions or speech to permit ‘procedural’ animation Expensive to define the vertex positions Non-realistic distortions as the vertices take different paths http://ivizlab.sfu.ca/research/iface
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Place markers on the human body Surround body with (at least 8) cameras Position of each marker inferred if visible to at least 2 cameras Rapid acquisition of motion
Active markers to avoid ‘marker swapping’
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