Pose Space Deformation: A unified approach to shape interpolation and skeleton-driven deformation J.P.Lewis, Matt Cordner, Nickson Fong Centropolis

Character animation Body: Face animation: “skeleton subspace deformation” Face animation: Shape interpolation (Tony de Peltrie, Star Wars, Dinosaur) Custom procedural models (Parke, Toy Story) Common practice for 10-15 years

Pose Space Deformation Combine direct geometric shape interpolation and skeleton driven deformation address the limitations of Shape Interpolation and Skeleton-driven deformation

Shape interpolation “Blend shapes, multi-target morphs, ” Weighted sum of key shapes Or delta shapes...

Shape interpolation (delta) delta shapes: equivalent! (combinations)

Shape Interpolation Advantages Disadvantages direct manipulation desired targets are achieved Disadvantages Superposition, not independent, linear subspace

Skeleton Subspace Deformation (SSD) “enveloping”, ... Symbolics, Softimage Weighted sum of surface point as transformed by various coordinate frames. Diagram

SSD problems: collapse

SSD problems Collapses, No direct manipulation, You can’t tell when you’re done

Goal Combine direct geometric shape interpolation and skeleton driven deformation BODY: use shape interpolation to control shoulder shape as it deforms according to the skeleton FACE: drive the face using jaw rotation rather than linear interpolation address the limitations of SI, SSD

Related work Combine skeletal and local deformation control Burtnyk and Wein, 1976

Related work: Idea #1 Animation as scattered interpolation Van Overveld, 1990; Litwinowicz & Williams 1994 Apply wide literature of interpolation directly to our animation problem!

Related work: Idea #2 Animation, etc. as general functional mapping Poggio & Brunelli 1992; Lewis 1988, 91

Synthesis attempt #1 Lewis 95: shape interpolation in the context of SSD

Related work Symbolics/Nichimen 91 Maya Interpolation Addition

Pose space deformation Surface cv movement Neck Joint R. Upper Arm Left Upper Arm Pose Space: N Dimensions Surface CV movement: 3 dimensions

Skeleton driven PSD elbow, f( rotation, load ) face is f( jaw rotation, emotion, phoneme...) quadruped leg/chest/neck

Scattered Interpolation Shepard Wiener interpolation, Kriging Others... Radial Basis functions universal approximation smooth if smooth kernel large literature Voronoi/delauney

VIDEO: Skeleton driven PSD

PSD vs. Shape Interpolation (SI) use same set of sculpted key shapes/delta shapes Shape Interpolation is superposition; PSD interpolates SI A B C crossfade is piecewise linear; PSD is smooth if desired

Shape Interpolation vs. PSD adds one dimension per shape not orthogonal animator manually solves for the representation interpolates shapes placed as desired in desired space

Shape Interpolation: reinforcement / fighting Adding smirk counteracts raise Dinosaur: 100+ face shapes + = raise smirk

PSD facial animation Delighted ? Serene Pleased <linear> Distressed <neutral>

VIDEO: PSD facial animation Aroused J.A.Russell, 1980 (simplified) alarmed delighted frustrated Displeasure Pleasure serene tired Sleepy

Conclusion Unification / simplification / modest improvement to existing common practice How many poses? Like shape interpolation, more is better, up to a point... Future: Learn the space? Example code: www.idiom.com/~zilla/PSD (september)

SSD Schematic Robot arm, two cylinders bent at the elbow

SSD Schematic

Related work Combine skeletal and local deformation control (Burtnyk and Wein, 1976) Animation as scattered interpolation (Van Overveld, 1990; Litwinowicz & Williams 1994) Animation as general functional mapping (Poggio & Brunelli 1992; Lewis 1988, 91) Lewis 95

PSD algorithm steps Definitions: pose, pose space Sculpt Define delta(pose) Solve Synthesize, evaluate, adjust, repeat

PSD vs. Shape Interpolation SI: adds, not orthogonal, one dimension per shape PSD: interpolates; shapes placed as desired in space

PSD/SI facial animation SI shapes define independent axes, PSD shapes are positioned as desired in desired space PSD: animator plans interpolation path. SI: animator also has to solve for this path in a non-orthogonal basis PSD is smooth (if desired)

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