IAM

07thOCTOBER2019

READING

Shiyu Liang, Yixuan Li, R. Srikant. Enhancing The Reliability of Out-of-distribution Image Detection in Neural Networks. ICLR 2018.

Liang et al. propose a perturbation-based approach for detecting out-of-distribution examples using a network’s confidence predictions. In particular, the approaches based on the observation that neural network’s make more confident predictions on images from the original data distribution, in-distribution examples, than on examples taken from a different distribution (i.e., a different dataset), out-distribution examples. This effect can further be amplified by using a temperature-scaled softmax, i.e.,

$ S_i(x, T) = \frac{\exp(f_i(x)/T)}{\sum_{j = 1}^N \exp(f_j(x)/T)}$

where $f_i(x)$ are the predicted logits and $T$ a temperature parameter. Based on these softmax scores, perturbations $\tilde{x}$ are computed using

$\tilde{x} = x - \epsilon \text{sign}(-\nabla_x \log S_{\hat{y}}(x;T))$

where $\hat{y}$ is the predicted label of $x$. This is similar to “one-step” adversarial examples; however, in contrast of minimizing the confidence of the true label, the confidence in the predicted label is maximized. This, applied to in-distribution and out-distribution examples is illustrated in Figure 1 and meant to emphasize the difference in confidence. Afterwards, in- and out-distribution examples can be distinguished using simple thresholding on the predicted confidence, as shown in various experiment, e.g., on Cifar10 and Cifar100.

Figure 1: Illustration of the proposed perturbation to amplify the difference in confidence between in- and out-distribution examples.

Also find this summary on ShortScience.org.

What is your opinion on the summarized work? Or do you know related work that is of interest? Let me know your thoughts in the comments below: