通过量化视觉证据等级,有效减少大模型幻觉生成。
ReWEIGH the Evidence: Calibrating Token-Level Ordinal Visual Evidence to Mitigate Hallucinations in Large Vision-Language Models

- 用视觉位置的词汇排名聚合证据,实现可比性归一化。
- 在四个7B模型上降低21.3%的幻觉物体提及率。
- 无需训练、低延迟,适配多种大模型架构。
大型视觉语言模型常产生图像不支持的内容。为在解码时防止此类内容,需对当前候选词提供图像支持强度的特定度量。模型的视觉-词元状态天然提供了这种证据来源,因其输出头投影可揭示各位置偏好的词汇项。由于不同视觉位置的概率幅度不可直接比较,不能直接聚合。词汇排名提供了一种尺度不变的聚合基础,但词元仍存在系统性排名差异。本文提出ReWEIGH,一种无需训练的解码干预方法:跨视觉位置聚合排名,并将每个候选与从无标签图像中估计的词元特异性参考值比较。推理时,ReWEIGH在预填充阶段缓存图像证据,仅对低于参考值的候选施加有限惩罚。在四个7B骨干模型上,幻觉物体提及减少最多达21.3%,同时基本保持或提升描述性和通用性能。证据缓存后,平均额外延迟仅为每词元1.33%,且效果扩展至六类架构、32B参数规模。
原文摘要 · Abstract (English)
Large vision-language models (LVLMs) often hallucinate, generating content that the input image does not support. Preventing such content during decoding calls for a candidate-specific measure of how strongly the image supports the token under consideration. The model's visual-token states offer a natural source of this evidence because projecting each state through the output head reveals which vocabulary items that position favors. These position-wise readouts cannot be pooled directly because their probability magnitudes are not comparable across visual positions. Vocabulary ranks provide a scale-invariant basis for pooling, but tokens still differ systematically in their typical rank-based evidence. We propose ReWEIGH, a training-free decoding intervention that aggregates these ranks across visual positions and compares each candidate with a token-specific reference estimated from unlabeled images. At inference, ReWEIGH caches the image evidence during prefill and applies a bounded penalty only to candidates that fall below their reference. On four 7B backbones, ReWEIGH reduces hallucinated object mentions by up to 21.3% while largely preserving or improving descriptive and general performance. With evidence cached, the average added latency is 1.33% per token, and the reductions extend across six architecture families to 32B parameters.
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