arXiv:2502.03566cs.CVcs.LG2025-02被引 28

CLIP其实能识别属性与对象的绑定关系,只是跨模态对齐出了问题。

CLIP Behaves like a Bag-of-Words Model Cross-modally but not Uni-modally

  • CLIP在单模态下已编码属性-对象绑定信息
  • 跨模态对齐失败导致绑定关系丢失,影响下游任务
  • 加个轻量线性层就能修复,无需重新训练模型

CLIP在多种下游任务中广泛应用,但近期研究质疑其对组合概念的表征能力。这些工作认为CLIP常表现为词袋(BoW)模型,将图像和文本视为独立概念集合,无法理解结构关系,尤其在多对象场景下难以正确绑定属性与对象。本文探究该现象的原因,发现关键在于跨模态对齐失败,而非缺乏绑定信息。通过线性探测、物体数量增加的鲁棒性测试及合取搜索实验,我们证实属性-对象绑定信息已存在于CLIP的文本与图像嵌入中。仅需对文本嵌入施加简单线性变换即可实现跨模态访问,显著提升绑定性能,证明原始信息已存在于单模态表示中。实际应用中,仅需在现有嵌入上添加轻量线性层即可优化系统,避免昂贵的编码器重训练。代码已公开于https://github.com/kdariina/CLIP-not-BoW-unimodally。

原文摘要 · Abstract (English)

CLIP (Contrastive Language-Image Pretraining) has become a popular choice for various downstream tasks. However, recent studies have questioned its ability to represent compositional concepts effectively. These works suggest that CLIP often acts like a bag-of-words (BoW) model, interpreting images and text as sets of individual concepts without grasping the structural relationships. In particular, CLIP struggles to correctly bind attributes to their corresponding objects when multiple objects are present in an image or text. In this work, we investigate why CLIP exhibits this BoW-like behavior. Our key finding is that CLIP does not lack binding information. Through linear probing, robustness tests with increasing object counts, and conjunctive search experiments, we show that attribute-object bindings are already encoded within CLIP's text and image embeddings. The weakness lies in the cross-modal alignment, which fails to preserve this information. We show it can be accessed cross-modally with a simple linear transformation to text embeddings. This improves CLIP's attribute-object binding performance and confirms that the information was already encoded unimodally. In practice, this means CLIP-based systems can be enhanced with a lightweight linear layer trained on existing embeddings, avoiding costly encoder retraining. The code is available at https://github.com/kdariina/CLIP-not-BoW-unimodally.

CLIP多模态语义绑定

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