Normal Image Guided Segmentation Framework for Unsupervised Anomaly Detection

Unsupervised anomaly detection is required to detect/segment anomalous samples/regions that deviate from the normal pattern while learning only through the normal sample category. Towards this end, this paper proposes a novel framework for anomaly detection by introducing normal images as guidance called Normal Image Guided Segmentation Framework (NIGSF). It consists of a Normal Guided Network (NGN) and a Saliency Augmentation Module (SAM). NGN constructs the contrast set, which is a candidate set for extracting normal sample features. Then, a normal feature extractor is developed to extract detailed and complete features containing normal semantic information as guidance features. Meanwhile, the guidance feature fusion module is introduced to realize normal semantic guidance in the feature space, and then the segmentation module discriminates the features that are different from the normal guidance features as anomalies. SAM aims to generate forged anomaly samples utilizing available normal samples. It introduces saliency maps and random Perlin noise to generate saliency Perlin noise maps and then to generate diverse forged anomaly samples. Extensive experiments are conducted to evaluate the performance of NIGSF on three anomaly detection benchmark datasets. The results demonstrate the effectiveness of each proposed module and the superiority of the proposed method. Specifically, NIGSF outperforms the runner-up by 5.4% in terms of anomaly segmentation AP metric.