Animation From Observation: Motion Editing Dan Kong CMPS 260 Final Project

Why we need motion editing Why we need motion editing Reuse motion capture data to different character and different actionsReuse motion capture data to different character and different actions Create infeasible motion which is hard to get by using motion captureCreate infeasible motion which is hard to get by using motion capture Change of intent which can not be predicted before the motion caputreChange of intent which can not be predicted before the motion caputre

In this project, I will implement a prototype motion editing system that has the following features Multiresolution motion filteringMultiresolution motion filtering Multitarget motion interpolationMultitarget motion interpolation Motion path editingMotion path editing

What is Motion Multiresolution filtering Basically, it is a technique that originally used in image processing now applied to the motion parameters of an articulated figure.Basically, it is a technique that originally used in image processing now applied to the motion parameters of an articulated figure. Intuition of this method: low frequencies contain gross and smooth motion while high frequencies contain detail, abrupt motion and most of the noise.Intuition of this method: low frequencies contain gross and smooth motion while high frequencies contain detail, abrupt motion and most of the noise.

Motion filtering algorithm The number of frames determine how many frequency bands (fb) for each signal: let 2 n < m < 2 n+1, then fb = n.The number of frames determine how many frequency bands (fb) for each signal: let 2 n < m < 2 n+1, then fb = n. Calculate the low-pass sequence of all fb signal by convolving the signal with a low-pass filter, obtaining G k, G k-1...G 0 where G fb is the DC component of the signal (0=<k<=fb)Calculate the low-pass sequence of all fb signal by convolving the signal with a low-pass filter, obtaining G k, G k-1...G 0 where G fb is the DC component of the signal (0=<k<=fb) Obtain the band- pass filter bands: L k = G k – G k+1Obtain the band- pass filter bands: L k = G k – G k+1

Motion filtering algorithm (continued) Adjust gains for each band and multiply L k by their current gain values.Adjust gains for each band and multiply L k by their current gain values. Reconstruct the motion signal:Reconstruct the motion signal: G 0 = G fb + G 0 = G fb +

Multitarget motion interpolation A process widely used in computer animation to blend between different models.A process widely used in computer animation to blend between different models. Facial animation: By blending the corresponding parameters of different face, we can control the expression.Facial animation: By blending the corresponding parameters of different face, we can control the expression. A happy walk + a sad walk = ?A happy walk + a sad walk = ?

Multitarget motion interpolation (continued) Mix multitarget interpolation and multiresolution filtering to blend the frequency bands of two or more motion separately.Mix multitarget interpolation and multiresolution filtering to blend the frequency bands of two or more motion separately. Need to establish the time correspondence between two signals.Need to establish the time correspondence between two signals.

Motion path editing What is path editing: – –Altering previously motion capture data to follow a different path Why Path Editing: - Using original motion in a new environment - Dynamic application: walking to a goal location

Alternative Approach Capture all desired motionsCapture all desired motions Disadvantages of this approach:Disadvantages of this approach: - Can not possible predict every possible required motion - Can not possible predict every possible required motion - Such a motion library are expensive to create - Such a motion library are expensive to create - Unwieldy to control as it expands - Unwieldy to control as it expands

Algorithm Overview Basic Idea:Basic Idea: Represent the motion relative to the path. As the path is altered, the orientation of character updates accordingly. Represent the motion relative to the path. As the path is altered, the orientation of character updates accordingly. AlgorithmAlgorithm - Automatic path generation - Automatic path generation - Calculate initial path coordinate system - Calculate initial path coordinate system - Path Editing - Path Editing - Computing the changed path coordinate system - Computing the changed path coordinate system

Why B-SplineWhy B-Spline –Local control without affecting global shape –continuous Path Coordinate RepresentationPath Coordinate Representation - p(t) is the coordinate center. The corresponding - p(t) is the coordinate center. The corresponding transformation matrix is P(t) transformation matrix is P(t) - R(t) is the orientation of the coordinate system. - R(t) is the orientation of the coordinate system. - P(t)R(t) is the path’s coordinate system - P(t)R(t) is the path’s coordinate system - R(t) -1 P(t) -1 is the transformation from global to path’s - R(t) -1 P(t) -1 is the transformation from global to path’s local coordinate system local coordinate system Path Description

Initial Path Generation Least-Square FittingLeast-Square Fitting –Using the root translation as the fitting point. –Compute average Y translation to constrain the path to lie in X-Z plane. path to lie in X-Z plane. –Store the R 0 (t) -1 P 0 (t) -1 for later editing

Path Editing After Altering the curveAfter Altering the curve –P(t)R(t) R 0 (t) -1 P 0 (t) -1 is computed as the coordinate system for the new path coordinate system for the new path –Once the P(t) is updated, the corresponding R(t) must be computed accordingly must be computed accordingly

Future Work Generate more frames when the path is strechedGenerate more frames when the path is streched Add constraint to avoid geometric violation.Add constraint to avoid geometric violation.

References “Motion Path Editing” “Motion Signal Processing” “Motion Warping” “Multiresolution Curves” “Hierarchical B-Spline refinement”

Thanks!!!