Learning Memory-guided Normality for Anomaly Detection (2003.13228v1)

Abstract: We address the problem of anomaly detection, that is, detecting anomalous events in a video sequence. Anomaly detection methods based on convolutional neural networks (CNNs) typically leverage proxy tasks, such as reconstructing input video frames, to learn models describing normality without seeing anomalous samples at training time, and quantify the extent of abnormalities using the reconstruction error at test time. The main drawbacks of these approaches are that they do not consider the diversity of normal patterns explicitly, and the powerful representation capacity of CNNs allows to reconstruct abnormal video frames. To address this problem, we present an unsupervised learning approach to anomaly detection that considers the diversity of normal patterns explicitly, while lessening the representation capacity of CNNs. To this end, we propose to use a memory module with a new update scheme where items in the memory record prototypical patterns of normal data. We also present novel feature compactness and separateness losses to train the memory, boosting the discriminative power of both memory items and deeply learned features from normal data. Experimental results on standard benchmarks demonstrate the effectiveness and efficiency of our approach, which outperforms the state of the art.

Learning Memory-guided Normality for Anomaly Detection

The paper "Learning Memory-guided Normality for Anomaly Detection" by Hyunjong Park, Jongyoun Noh, and Bumsub Ham explores a novel approach to anomaly detection in video sequences using a memory-augmented architecture. The focus is on augmenting convolutional neural networks (CNNs) with a memory module to explicitly consider the diversity of normal patterns while alleviating the representation capability that often reconstructs abnormalities as well.

Summary of the Paper

Traditional CNN-based anomaly detection approaches often leverage proxy tasks like frame reconstruction, leading to issues like reconstructing abnormal patterns due to the expressive power of CNNs. This work proposes an unsupervised learning framework incorporating a memory module that records prototypical normal patterns using an update scheme. Features learned from video frames are matched against these memory items to determine normality, with the diversity and compactness of feature representation being key aspects enhanced by the memory module.

Key Contributions

1. Memory Module Integration: The memory module stores multiple prototype patterns, enabling the model to recognize a broad range of normal patterns without ambiguous overlaps with abnormal ones.
2. Feature Compactness and Separateness Loss: These novel losses ensure that the features of normal data are compact and discriminative by promoting proximity to the nearest memory item and separation from the second closest, thereby enhancing feature diversity.
3. Dynamic Memory Update: The approach incorporates a strategy to update memory with normal patterns even at test time while preventing abnormalities within the memory using a weighted regular score.

Experimental Results

Statistically significant improvements were recorded over existing methods across several benchmark datasets: UCSD Ped2, CUHK Avenue, and ShanghaiTech. Notably, on UCSD Ped2 and CUHK Avenue, their model achieves new state-of-the-art performance. The employment of both reconstruction and prediction tasks, with the latter achieving 97.0% AUC on Ped2, highlights the efficiency of their method.

Implications and Future Directions

Practically, this approach lends itself well to anomaly detection tasks in video surveillance, where capturing a range of normal activities is crucial. Theoretically, it suggests that augmenting neural networks with auxiliary memory can effectively separate complex patterns, pushing forward methodologies in unsupervised learning.

Future work could explore scaling this method to handle even larger datasets or integrating the memory framework into other neural network architectures. Continued research may also involve refining the dynamic memory update strategies and investigating applications beyond video surveillance.

In conclusion, this work contributes a well-defined memory-guided paradigm to anomaly detection, effectively managing the complexity of pattern diversity without explicit abnormal data, thereby providing a robust framework for future developments in this domain.