Unsupervised Accuracy Estimation of Deep Visual Models using Domain-Adaptive Adversarial Perturbation without Source Samples

Deploying deep visual models can lead to performance drops due to the discrepancies between source and target distributions. Several approaches leverage labeled source data to estimate target domain accuracy, but accessing labeled source data is often prohibitively difficult due to data confidentiality or resource limitations on serving devices. Our work proposes a new framework to estimate model accuracy on unlabeled target data without access to source data. We investigate the feasibility of using pseudo-labels for accuracy estimation and evolve this idea into adopting recent advances in source-free domain adaptation algorithms. Our approach measures the disagreement rate between the source hypothesis and the target pseudo-labeling function, adapted from the source hypothesis. We mitigate the impact of erroneous pseudo-labels that may arise due to a high ideal joint hypothesis risk by employing adaptive adversarial perturbation on the input of the target model. Our proposed source-free framework effectively addresses the challenging distribution shift scenarios and outperforms existing methods requiring source data and labels for training.

Self-Supervised Contrastive Representation Learning for 3D Mesh Segmentation

3D deep learning is a growing field of interest due to the vast amount of information stored in 3D formats. Triangular meshes are an efficient representation for irregular, non-uniform 3D objects. However, meshes are often challenging to annotate due to their high geometrical complexity. Specifically, creating segmentation masks for meshes is tedious and time-consuming. Therefore, it is desirable to train segmentation networks with limited-labeled data. Self-supervised learning (SSL), a form of unsupervised representation learning, is a growing alternative to fully-supervised learning which can decrease the burden of supervision for training. We propose SSL-MeshCNN, a self-supervised contrastive learning method for pre-training CNNs for mesh segmentation. We take inspiration from traditional contrastive learning frameworks to design a novel contrastive learning algorithm specifically for meshes. Our preliminary experiments show promising results in reducing the heavy labeled data requirement needed for mesh segmentation by at least 33%.

Analytic Mutual Information in Bayesian Neural Networks

Bayesian neural networks have successfully designed and optimized a robust neural network model in many application problems, including uncertainty quantification. However, with its recent success, information-theoretic understanding about the Bayesian neural network is still at an early stage. Mutual information is an example of an uncertainty measure in a Bayesian neural network to quantify epistemic uncertainty. Still, no analytic formula is known to describe it, one of the fundamental information measures to understand the Bayesian deep learning framework. In this paper, with the Dirichlet distribution assumption in its intermediate encoded message, we derive the analytical formula of the mutual information between model parameters and the predictive output by leveraging the notion of the point process entropy. Then, as an application, we discuss the estimation of the Dirichlet parameters and show its practical application in the active learning uncertainty measures.

PatchNet: Unsupervised Object Discovery based on Patch Embedding

We demonstrate that frequently appearing objects can be discovered by training randomly sampled patches from a small number of images (100 to 200) by self-supervision. Key to this approach is the pattern space, a latent space of patterns that represents all possible sub-images of the given image data. The distance structure in the pattern space captures the co-occurrence of patterns due to the frequent objects. The pattern space embedding is learned by minimizing the contrastive loss between randomly generated adjacent patches. To prevent the embedding from learning the background, we modulate the contrastive loss by color-based object saliency and background dissimilarity. The learned distance structure serves as object memory, and the frequent objects are simply discovered by clustering the pattern vectors from the random patches sampled for inference. Our image representation based on image patches naturally handles the position and scale invariance property that is crucial to multi-object discovery. The method has been proven surprisingly effective, and successfully applied to finding multiple human faces and bodies from natural images.

BABA: Beta Approximation for Bayesian Active Learning

This paper introduces a new acquisition function under the Bayesian active learning framework, namely BABA. It is motivated by previously well-established works BALD, and BatchBALD which capture the mutual information between the model parameters and the predictive outputs of the data. Our proposed measure, BABA, endeavors to quantify the normalized mutual information by approximating the stochasticity of predictive probabilities using Beta distributions. BABA outperforms the well-known family of acquisition functions, including BALD and BatchBALD. We demonstrate this by showing extensive experimental results obtained from MNIST and EMNIST datasets.

Highly Efficient Representation and Active Learning Framework for Imbalanced Data and its Application to COVID-19 X-Ray Classification

We propose a highly data-efficient classification and active learning framework for classifying chest X-rays. It is based on (1) unsupervised representation learning of a CNN (Convolutional Neural Network) and (2) the GP (Gaussian Process) method. The unsupervised representation learning employs self-supervision that does not require class labels, and the learned features are proven to achieve label-efficient classification. GP is a kernel-based Bayesian approach that also leads to data-efficient predictions with the added benefit of estimating each decision's uncertainty. Our novel framework combines these two elements in sequence to achieve highly data and label efficient classifications. Moreover, both elements are less sensitive to the prevalent and challenging class imbalance issue, thanks to the (1) feature learned without labels and (2) the Bayesian nature of GP. The GP-provided uncertainty estimates enable active learning by ranking samples based on the uncertainty and selectively labeling samples showing higher uncertainty. We apply this novel combination to the data-deficient and severely imbalanced case of COVID-19 chest X-ray classification. We demonstrate that only $\sim 10\%$ of the labeled data is needed to reach the accuracy from training all available labels. Its application to the COVID-19 data in a fully supervised classification scenario shows that our model, with a generic ResNet backbone, outperforms (COVID-19 case by 4\%) the state-of-the-art model with a highly tuned architecture. Our model architecture and proposed framework are general and straightforward to apply to a broader class of datasets, with expected success.