> ## Documentation Index
> Fetch the complete documentation index at: https://mirage-eval.com/llms.txt
> Use this file to discover all available pages before exploring further.

# CHAIR

> Hallucinated objects in captions.

CHAIR finds the object words in a caption and checks each one against the image's labels. CHAIR-I is the share of mentioned objects that are not in the image, so lower is better.

Paper: Rohrbach et al., "Object Hallucination in Image Captioning", EMNLP 2018. [arXiv:1809.02156](https://arxiv.org/abs/1809.02156)

## Modification: Mod-CHAIR

Mod-CHAIR counts nouns only, adds objects the judge saw in the image to the labels, and scores F0.5 of (1 - Mod-CHAIR-I) and coverage, the share of known objects the caption names. The change is needed because raw CHAIR-I rewards captions that name almost nothing and counts unlabelled objects like "sky" as hallucinations.


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