2022-09-26 更新

Oracle Analysis of Representations for Deep Open Set Detection

Authors:Risheek Garrepalli, Alan Fern, Thomas G. Dietterich

The problem of detecting a novel class at run time is known as Open Set Detection & is important for various real-world applications like medical application, autonomous driving, etc. Open Set Detection within context of deep learning involves solving two problems: (i) Must map the input images into a latent representation that contains enough information to detect the outliers, and (ii) Must learn an anomaly scoring function that can extract this information from the latent representation to identify the anomalies. Research in deep anomaly detection methods has progressed slowly. One reason may be that most papers simultaneously introduce new representation learning techniques and new anomaly scoring approaches. The goal of this work is to improve this methodology by providing ways of separately measuring the effectiveness of the representation learning and anomaly scoring. This work makes two methodological contributions. The first is to introduce the notion of Oracle anomaly detection for quantifying the information available in a learned latent representation. The second is to introduce Oracle representation learning, which produces a representation that is guaranteed to be sufficient for accurate anomaly detection. These two techniques help researchers to separate the quality of the learned representation from the performance of the anomaly scoring mechanism so that they can debug and improve their systems. The methods also provide an upper limit on how much open category detection can be improved through better anomaly scoring mechanisms. The combination of the two oracles gives an upper limit on the performance that any open category detection method could achieve. This work introduces these two oracle techniques and demonstrates their utility by applying them to several leading open category detection methods.


Understanding Open-Set Recognition by Jacobian Norm of Representation

Authors:Jaewoo Park, Hojin Park, Eunju Jeong, Andrew Beng Jin Teoh

In contrast to conventional closed-set recognition, open-set recognition (OSR) assumes the presence of an unknown class, which is not seen to a model during training. One predominant approach in OSR is metric learning, where a model is trained to separate the inter-class representations of known class data. Numerous works in OSR reported that, even though the models are trained only with the known class data, the models become aware of the unknown, and learn to separate the unknown class representations from the known class representations. This paper analyzes this emergent phenomenon by observing the Jacobian norm of representation. We theoretically show that minimizing the intra-class distances within the known set reduces the Jacobian norm of known class representations while maximizing the inter-class distances within the known set increases the Jacobian norm of the unknown class. The closed-set metric learning thus separates the unknown from the known by forcing their Jacobian norm values to differ. We empirically validate our theoretical framework with ample pieces of evidence using standard OSR datasets. Moreover, under our theoretical framework, we explain how the standard deep learning techniques can be helpful for OSR and use the framework as a guiding principle to develop an effective OSR model.


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