multi-camera tracking of articulated human motion using motion and shape cues
Post on 14-Jan-2016
19 Views
Preview:
DESCRIPTION
TRANSCRIPT
Multi-camera Tracking of Articulated Human Motion using Motion and Shape Cues
Aravind Sundaresan and Rama Chellappa
Center for Automation ResearchUniversity of Maryland, College Park MD
USA
What is motion capture?
Motion capture (Mocap) is the process of analysing and expressing human motion in mathematical terms. Initialisation, Pose estimation and Tracking.
Applications Motion Analysis for clinical studies, Human-
computer interaction, Computer animation.
Marker-based systems have shortcomings Cumbersome, introduce artefacts, time
consuming.
Marker-less system desirable.
Calibration and Human body model
Use multiple cameras (8) in our capture 640x480 grey scale images at 30 fps. Calibrated using algorithm of Svoboda.
Use articulated human body model. Super-quadrics for body segments. Model described by joint locations and super-
quadrics. Pose is described by joint angles.
Overview
Use images from multiple cameras. Compute 2-D pixel displacement between t and
t+1. Predict 3-D pose at t+1 using pixel displacement. Compute spatial energy function as function of
pose. Minimise energy function to obtain pose at t+1.
Tracking Framework
Use motion and spatial cues for tracking. Motion cues use texture.
Error accumulation: estimates only change in pose. Spatial cues obtained from silhouettes, edges,
etc. Instability: Solutions are stable only “locally”.
Predictor-Corrector framework. Predictor:
Compute motion(t) from pixel displacement. Predict pose(t+1) from pose(t) and motion(t).
Corrector: Assimilate spatial cues into single energy function. Correct pose(t+1) by minimising energy function.
Pixel registration and displacement
Project model onto image to obtain Body part label for pixel. 3-D location of pixel. Mask for each body part
Find dense pixel correspondence using Parametric optical flow-based algorithm for each
segment.. Minimise MSE:
Pose from pixel displacement
State-space formulation
Linearisation We show that Taylor series Iteratively estimate pose
Combine spatial cues
Combine multiple spatial cues into a single “spatial energy function”.Compute pose energy as function of dx, dy and Φ.
+ =
Minimise 3D pose energy
Given multiple views and 3-D pose Compute 2-D pose for ith image Compute Ei for ith camera using 2-D pose 3D pose energy, E = E
1+ E
2 + ... + E
n Compute minimum energy pose using
optimisation.
Tracking results
top related