Progressive prediction: Video anomaly detection via multi-grained prediction

Video Anomaly Detection (VAD) has been an active research field for several decades. However, most existing approaches merely extract a single type of feature from videos and define a single paradigm to indicate the extent of abnormalities. A coarse-to-fine three-level prediction is built by integrating different levels of spatio-temporal representations, better highlighting the difference between normal and abnormal behaviors. First, an object-level trajectory prediction is proposed to model human historical position using a graph transformer network. Subsequently, skeleton-level prediction is achieved by incorporating the positional information from the trajectory prediction. More importantly, based on the predicted skeleton, a skeleton-guided pixel-level region prediction is performed. A novel Skeleton Conditioned Generative Adversarial Network (SCGAN) is designed to explore the correlation between skeleton-level and pixel-level motion prediction. Benefiting from SCGAN, the prediction of human regions is contributed by both coarse-grained and fine-grained motion features. This three-level prediction, namely Progressive Prediction Video Anomaly Detection (P³VAD), enlarges the prediction error on irregular motion patterns. Besides, a pixel-level analysis method is proposed to achieve Background-bias Elimination (BE) and denoise the predicted region. Experimental results validate the effectiveness of P³VAD on the four benchmark datasets (ShanghaiTech, CUHK Avenue, IITB-Corridor, and ADOC).