Multi-Prompt Progressive Alignment for Multi-Source Unsupervised Domain Adaptation

TL;DR

This paper introduces MP^2A, a progressive alignment method for multi-source unsupervised domain adaptation using CLIP, which gradually incorporates target samples to improve robustness and achieve state-of-the-art results.

Contribution

The paper proposes a novel progressive alignment strategy for CLIP-based multi-source UDA, addressing noise and domain gap issues more effectively than existing one-shot methods.

Findings

MP^2A outperforms recent CLIP-based MS-UDA methods on benchmarks.

Gradual sample incorporation improves domain-invariant feature learning.

Method demonstrates robustness against noisy and hard-to-classify samples.

Abstract

Large Vision-Language Models like CLIP have become a powerful foundation for Unsupervised Domain Adaptation due to their strong zero-shot generalization. State-of-the-art methods typically leverage CLIP to generate pseudo-labels for the target domain, then fine-tune the model to learn domain-invariant features. However, these methods attempt to align source and target domains using all pseudo-labeled data simultaneously. This one-shot alignment struggles with noisy, hard-to-classify samples, leading to error propagation and suboptimal feature learning. The problem is even more amplified in the multi-source scenario, where diverse domain gaps and varying noise levels across multiple source domains further destabilize the alignment process. To address this issue, in this work, we propose a progressive alignment strategy for adapting CLIP to unlabeled downstream task. Our method begins by training the model on a high-confidence subset of target samples, allowing it to first learn a well-aligned representation from the most reliable data. As training progresses, it gradually incorporates more challenging samples, guiding the model to refine its understanding without being overwhelmed by initial label noise. This progressive approach effectively mitigates confirmation bias and promotes a more robust convergence, allowing for the learning of genuinely domain-invariant features. We name our approach MP^2A and test it on three popular UDA benchmarks, namely ImageCLEF, Office-Home, and the most challenging DomainNet. Experiments showcase that MP^2A achieves state-of-the-art performance when compared with most recent CLIP-based MS-UDA approaches, demonstrating the effectiveness of our approach.