Home > Uncategorized > Coherent Filtering: Detecting Coherent Motions from Crowd Clutter

Coherent Filtering: Detecting Coherent Motions from Crowd Clutter

Coherent motion is a universal phenomenon in nature and widely exists in many physical and biological systems. For example, the tornadoes, storms and atmospheric circulation are all caused by the coherent movements of physical particles in the atmosphere. Meanwhile, the collective behaviors of organisms such as schooling fishes and pedestrian crowd have long captured the interests of social and natural scientists. Here are examples of coherent motions in videos.

Figure 1: Coherent motions in nature.

Detecting these coherent motion patterns in crowd is the first step to organize the low-level features into semantic clusters. It will benefit high-level tasks such as scene understanding and activity analysis.

Recently I proposed a simple coherent motion detection technique called Coherent Filtering. It is published in Proceedings of 12th European Conference on Computer Vision (ECCV 2012). It is a generic clustering algorithm for analyzing time-series signals.

In our formulation, the low-level features are the keypoint trajectories (short time-series) automatically extracted from crowd video. Here are examples of the keypoint trajectories extracted from the crowd videos.

Figure 2. A) One frame of the crowd videos. B) The trajectories extracted from the videos. Colors of trajectories are randomly assigned.

Since the scenes in video are very crowded, there will be lots of dynamic noises and cluttered trajectories. Thus the purpose of the technique is to remove these noises and cluster keypoint trajectories into different coherent motion patterns. Here are some clustering results:

Figure 3. The coherent motion detection results by Coherent Filtering. Keypoints with the same color belong to the same coherent motion pattern.

The mechanism behind our technique is that it is based on a prior discovered in the particle dynamics called Coherent Neighbor Invariance. The details can be found at the project page and technical paper.

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