Normalizing Flows for Human Pose Anomaly Detection
This work addresses video anomaly detection for surveillance or safety applications by improving accuracy and fairness, though it is incremental as it builds on normalizing flows for a specific domain.
The paper tackles human pose anomaly detection in videos by focusing on pose graphs to reduce nuisance parameters and bias, achieving state-of-the-art results on the ShanghaiTech and UBnormal datasets with a lightweight model of about 1K parameters.
Video anomaly detection is an ill-posed problem because it relies on many parameters such as appearance, pose, camera angle, background, and more. We distill the problem to anomaly detection of human pose, thus decreasing the risk of nuisance parameters such as appearance affecting the result. Focusing on pose alone also has the side benefit of reducing bias against distinct minority groups. Our model works directly on human pose graph sequences and is exceptionally lightweight (~1K parameters), capable of running on any machine able to run the pose estimation with negligible additional resources. We leverage the highly compact pose representation in a normalizing flows framework, which we extend to tackle the unique characteristics of spatio-temporal pose data and show its advantages in this use case. The algorithm is quite general and can handle training data of only normal examples as well as a supervised setting that consists of labeled normal and abnormal examples. We report state-of-the-art results on two anomaly detection benchmarks - the unsupervised ShanghaiTech dataset and the recent supervised UBnormal dataset.