Andrew P. Witkin

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A snake is an energy-minimizing spline guided by external constraint forces and influenced by image forces that pull it toward features such as lines and edges. Snakes are active contour models: they lock onto nearby edges, localizing them accurately. Scale-space continuation can be used to enlarge the capture region surrounding a feature. Snakes provide a(More)
The bottle-neck in most cloth simulation systems is that time steps must be small to avoid numerical instability. This paper describes a cloth simulation system that can stably take large time steps. The simulation system couples a new technique for enforcing constraints on individual cloth particles with an implicit integration method. The simulator models(More)
The extrema in a signal and its first few derivatives provide a useful general-purpose qualitative description for many kinds of signals. A fundamental problem in computing such descriptions is scale: a derivative must be taken over some neighborhood, but there is seldom a principled basis for choosing its size. Scale-space filtering is a method that(More)
Spacetime constraints are a new method for creating character animation. The animator specifies <i>what</i> the character has to do, for instance, "jump from here to there, clearing a hurdle in between;" <i>how</i> the motion should be performed, for instance "don't waste energy," or "come down hard enough to splatter whatever you land on;" the character's(More)
Oriented patterns, such as those produced by propagation, accretion, <>r deformation, ore common in nature and therefore an important class for visual analysis. Our approach to understanding such patterns is to decompose them into two parts: a flow field, describing the direction of anisotropy, and the residual pattern obtained by describing the image in a(More)
We introduce a novel algorithm for transforming character animation sequences that preserves essential physical properties of the motion. By using the spacetime constraints dynamics formulation our algorithm maintains realism of the original motion sequence without sacrificing full user control of the editing process. In contrast to most physically based(More)
We describe a simple technique for editing captured or keyframed animation based on warping of the motion parameter curves. The animator interactively defines a set of keyframe-like constraints which are used to derive a smooth deformation that preserves the fine structure of the original motion. Motion clips are combined by overlapping and blending of the(More)
We present a new approach to interactive modeling of freeform surfaces. Instead of a fixed mesh of control points, the model presented to the user is that of an infinitely malleable surface, with no fixed controls. The user is free to apply control points and curves which are then available as handles for direct manipulation. The complexity of the surface’s(More)