Paper Detail

CAPEval: A Decoupled Caption Evaluation across Understanding and Generation

Zhipeng Liu, Haochen Wang, Zhaoxiang Zhang

arxiv Score 10.8

Published 2026-08-03 · First seen 2026-08-04

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Abstract

Captions serve as a primary supervision signal for both multimodal understanding and text-to-image generation. However, previous evaluations treat the caption quality as a single scalar objective, which conflates two distinct properties: (1) how much visual information a caption covers and (2) how reliably the image supports its stated claims. To this end, we design a decoupled caption evaluation benchmark, CAPEval (Coverage And Precision Evaluation), with human-written ground-truth captions and human-verified atomic checklist items. Specifically, CAPEval decomposes caption quality into Coverage and Precision. The former quantifies how thoroughly a caption covers ground-truth factual content, while the latter reflects the factual correctness rate of all claims expressed in the caption. We select 10 captioners and further conduct controlled downstream end-to-end experiments with them from four model families, where the caption source is the only variable. Empirically, we find a consistent task-dependent dissociation: Coverage serves as the stronger correlate for understanding performance, whereas Precision acts as the dominant predictor for generation performance. This decoupled evaluation paradigm not only delivers a more fine-grained diagnosis of caption quality, but also offers actionable guidance for selecting and optimizing captioners tailored to different downstream tasks.

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BibTeX

@article{liu2026capeval,
  title = {CAPEval: A Decoupled Caption Evaluation across Understanding and Generation},
  author = {Zhipeng Liu and Haochen Wang and Zhaoxiang Zhang},
  year = {2026},
  abstract = {Captions serve as a primary supervision signal for both multimodal understanding and text-to-image generation. However, previous evaluations treat the caption quality as a single scalar objective, which conflates two distinct properties: (1) how much visual information a caption covers and (2) how reliably the image supports its stated claims. To this end, we design a decoupled caption evaluation benchmark, CAPEval (Coverage And Precision Evaluation), with human-written ground-truth captions and},
  url = {https://arxiv.org/abs/2608.02589},
  keywords = {cs.CV, code available, huggingface daily},
  eprint = {2608.02589},
  archiveprefix = {arXiv},
}

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