Model Recycling Framework for Multi-Source Data-Free Supervised Transfer Learning

This situation can give rise to privacy concerns, as organizations may not want to share sensitive information; for instance, healthcare providers may be reluctant to share patient information and security system maintainers may not want to risk sharing facial recognition data for system performance updates. Additionally, there may be issues with obtaining the source data such as when it is hard to retrieve due to technical difficulties or intellectual property restrictions (Li et al., 2020b; Chen et al., 2021; Liang et al., 2020; Ahmed et al., 2021b). Recent advancements in source-free unsupervised domain adaptation (SFUDA) have presented solutions for a scenario where source data is not accessible (Fang et al., 2022). Purposely, SFUDA utilizes pre-trained source models to improve the generalization of a model on an unlabeled target dataset. Our work is similar to other approaches in the field of SFUDA (Li et al., 2020b; Chen et al., 2021; Liang et al., 2020; Ahmed et al., 2021b), in that it addresses the practical scenario where source data is not available during training. Importantly, a crucial aspect is often overlooked by the majority of SFUDA studies. When it is assumed that source data is not accessible, then it cannot be guaranteed that the available source models have been trained on domains related to the target task. And yet, most of the works only have experimented on classic domain adaptation benchmarks, which are somewhat related by design, e.g., Digits-Five (Peng et al., 2019), Office-31 (Saenko et al., 2010), and Office-Home (Venkateswara et al., 2017), i.e,, domains that share the same labels but are dissimilar in feature (and ambient) space. Our approach is unique in that we consider such a source-free supervised transfer learning (SFSTL) setting (Lee et al., 2019), where we do not assume source models are trained on tasks with similar feature spaces or 1