Multiple-Instance feature extraction at the bag and instance levels using the maximum trace-difference criterion

Multiple-Instance Learning (MIL) refers to the problem wherein each object is a bag consisting of multiple instances and only the bags' labels are provided. MIL data can contain irrelevant, redundant, and noisy components, which makes feature-extraction preprocessing essential for performance improvement. In this paper, we propose a Multiple-Instance Feature Extraction (MIFE) framework to design algorithms at both the bag and instance levels based on the Maximum Trace-Difference criterion, which simultaneously maximizes between-class scattering and minimizes within-class scattering. MIFE not only treats the existing Multiple-Instance Discriminant Analysis algorithm as an instance-level realization but also enables us to adopt different bag-level distances to design corresponding bag-level algorithms. In particular, we introduce the Class-to-Bag (C2B) and Bag-to-Bag (B2B) distances into the MIFE framework and obtain the MIFE-C2B and MIFE-B2B algorithms, respectively. The experimental results show that both MIFE-C2B and MIFE-B2B obtain competitive classification performance, and MIFE-B2B obtains the best performance on most tested datasets. The dimensionality reduction results show that both MIFE-C2B and MIFE-B2B obtain their best performance with no more than approximately 30% of the original dimensions on most tested datasets.