用最优传输统一视觉语言模型的推理与自适应目标,提升泛化能力。
From Inference to Adaptation: A Unified Optimal Transport View of Vision Language Model

- 基于最优传输构建样本级伪标签,增强推理鲁棒性。
- 通过软标签InfoNCE损失实现细粒度跨模态对齐,性能提升7%。
- 理论证明信息瓶颈损失可重写为最优传输形式,实现目标统一。
视觉语言模型(VLM)在零样本场景下表现优异,但在实际分布偏移下仍敏感。现有测试时自适应方法依赖噪声较大的原始嵌入相似度生成伪标签,易受分布偏移影响。为此,本文提出一种统一框架 extsc{Algname},将零样本图像分类建模为基于Wasserstein最优传输的跨模态对齐问题,生成更可靠的样本级伪标签。在自适应阶段,采用软标签InfoNCE损失,利用最优传输诱导的伪标签进行对比学习,显式建模图像-文本对间的细粒度关系,从而实现精准推理。理论分析表明,InfoNCE损失可等价重构为Wasserstein OT形式,使推理与自适应目标一致,相互增益。大量实验验证了该方法的有效性与高效性,在多个基准上超越最佳基线达7%,且计算开销极低。
原文摘要 · Abstract (English)
Vision-language models (VLMs) have demonstrated remarkable zero-shot capabilities yet remain sensitive to real-world distribution shifts during inference. Although significant efforts are devoted to adapting VLMs at test time, they rely heavily on noisy pseudo-labels predicted directly from raw embedding similarities during inference, which are unreliable under distribution shift and mislead the adaptation. To avoid noise amplification, existing works craft coarse-grained surrogate objectives during adaptation, which fail to explicitly model sample-level relationships across different modalities, creating objective mismatch with inference, thus leading to marginal performance improvement. In this work, we aim to bridge the detached objectives of inference and adaptation for VLMs, and propose a principled VLM TTA method called \algname. For VLM inference, we formulate the zero-shot image classification task as a cross-modal alignment problem encoded via a Wasserstein OT formulation, providing robust pseudo-labels at the sample-level to effectively adapt VLMs. For VLM adaptation, we adopt a soft-label InfoNCE loss to adapt VLMs based on the OT-induced pseudo-labels, leveraging fine-grained supervisions to explicitly model relationships of individual image-text pairs via contrastive learning, which empowers accurate inference at the same granularity. Moreover, we theoretically reveal that the InfoNCE loss can be neatly reformulated as a Wasserstein OT formulation, thereby unifying the objectives of the inference and adaptation of VLMs to achieve their mutual benefits. Extensive experiments demonstrate the effectiveness and efficiency of our methods, outperforming the best-performing methods by up to 7% with state-of-the-art efficiency.
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