Bag-Level Aggregation for Multiple Instance Active Learning in Instance Classification Problems

TL;DR

This paper introduces novel bag-level aggregation methods for multiple instance active learning, significantly reducing labeling efforts in weakly annotated data scenarios like medical imaging and video analysis.

Contribution

It proposes two new bag-level aggregation techniques for multiple instance active learning that outperform existing methods in reducing query numbers.

Findings

Both methods outperform reference approaches in experiments.

Significant reduction in queries needed for comparable performance.

Effective handling of bag structure improves active learning efficiency.

Abstract

A growing number of applications, e.g. video surveillance and medical image analysis, require training recognition systems from large amounts of weakly annotated data while some targeted interactions with a domain expert are allowed to improve the training process. In such cases, active learning (AL) can reduce labeling costs for training a classifier by querying the expert to provide the labels of most informative instances. This paper focuses on AL methods for instance classification problems in multiple instance learning (MIL), where data is arranged into sets, called bags, that are weakly labeled. Most AL methods focus on single instance learning problems. These methods are not suitable for MIL problems because they cannot account for the bag structure of data. In this paper, new methods for bag-level aggregation of instance informativeness are proposed for multiple instance active learning (MIAL). The \textit{aggregated informativeness} method identifies the most informative instances based on classifier uncertainty, and queries bags incorporating the most information. The other proposed method, called \textit{cluster-based aggregative sampling}, clusters data hierarchically in the instance space. The informativeness of instances is assessed by considering bag labels, inferred instance labels, and the proportion of labels that remain to be discovered in clusters. Both proposed methods significantly outperform reference methods in extensive experiments using benchmark data from several application domains. Results indicate that using an appropriate strategy to address MIAL problems yields a significant reduction in the number of queries needed to achieve the same level of performance as single instance AL methods.