This paper introduces an algorithm for detecting walking
motion using point trajectories in video sequences. Given
a number of point trajectories, we identify those which are
spatio-temporally correlated as arising from feet in walking
motion. Unlike existing techniques we do not assume
clean point tracks but instead propose “probabilistic trajectories”
as new features to classify. These are extracted
from directed acyclic graphs whose edges represent temporal
point correspondences and are weighted with their
matching probability in terms of appearance and location.
This representation tolerates the inherent trajectory ambiguity,
for example due to occlusions. We then learn the
correlation between the movement of two feet using a random
forest classifier. The effectiveness of the algorithm is
demonstrated in experiments on image sequences captured
with a static camera.