Unsupervised anomaly detection is a challenging task utilizing autoencoders and generative models.
Autoencoders are often used to model normal data distribution and identify anomalies by high reconstruction error.
The proposed approach involves a decoupled training using both an autoencoder and a likelihood model with noise contrastive estimation (NCE).
NCE estimates a probability density function for anomaly scoring in the joint space of the autoencoder's latent representation and reconstruction quality features.
To improve NCE's false negative rate, reconstruction features are systematically varied during training to optimize the noise distribution.
Experimental assessments on multiple benchmark datasets show that the proposed approach matches the performance of leading anomaly detection algorithms.