Layer Precision Reduction for Deep Anomaly Detection

Autoencoders (AEs) are widely used in unsupervised anomaly detection (AD) due to their ability to model complex data distributions. However, their strong reconstruction capacity, while effective for capturing normal patterns, often enables them to also reconstruct anomalous objects, including both individual and collective anomalies, which reduces detection performance. This limitation is particularly severe for collective anomalies, which are frequently misinterpreted as normal clusters. To address this issue, we propose Layer Precision Reduction (LPR), a novel technique that systematically constrains the numerical precision of weights and biases in neural network layers to strategically reduce the learning capacity of neural networks, such as the reconstruction capacity of AEs. LPR encourages the network to prioritize dominant manifold structures while suppressing the reconstruction of rare or anomalous patterns. While LPR was primarily developed for AE-based detectors (the focus of this paper), it is applicable to any neural network. Simulations are conducted with 24 AD models across 30 real-world public datasets. LPR is applied to 10 deep AD models, including 5 unsupervised AE-based methods, 2 unsupervised non-AE-based methods, 1 semi-supervised method, 1 weakly supervised method, and 1 fully supervised method. LPR consistently improves all 10 models, most notably enhancing the best-performing unsupervised AE-based detector from an average AUROC of 72.12\% to 83.06\%, surpassing the strongest unsupervised non-AE-based competitor, which achieves an average AUROC of 77.36\%, across the remaining 14 detectors. These results reveal a previously unexplored link between layer-level numerical precision and manifold pattern prioritization, demonstrating that LPR serves as a simple yet powerful mechanism for enhancing AD performance while offering broad applicability to diverse neural architectures and potential extensions to tasks beyond AD.