BEiTScore++: Reference-free Image Captioning Evaluation with BEiT-3 and Conformalized Quantile Regression

Goncalo Emanuel Cavaco Gomes, Bruno Martins, Chrysoula Zerva


Abstract
Reliable uncertainty estimation is important for deploying evaluation metrics in real-world settings, where both input ambiguity and domain shifts are common. In this work, we propose an uncertainty-aware extension of the BEiTScore image captioning metric, producing calibrated confidence intervals alongside alignment scores. Our approach models predictive distributions over human judgments, enabling both accurate scoring and principled uncertainty quantification. We evaluate our BEiTScore++ metric across multiple benchmarks with human-annotated ratings, demonstrating strong performance in terms of ranking correlation, calibration, and interval sharpness. BEiTScore++ not only produces accurate predictions, but also captures aleatoric uncertainty arising from ambiguous inputs, and epistemic uncertainty due to limited model knowledge, making it a reliable tool for uncertainty-aware evaluation of image-caption alignment.
Anthology ID:
2026.findings-emnlp.2160
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
46192–46226
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.2160/
DOI:
Bibkey:
Cite (ACL):
Goncalo Emanuel Cavaco Gomes, Bruno Martins, and Chrysoula Zerva. 2026. BEiTScore++: Reference-free Image Captioning Evaluation with BEiT-3 and Conformalized Quantile Regression. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 46192–46226, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
BEiTScore++: Reference-free Image Captioning Evaluation with BEiT-3 and Conformalized Quantile Regression (Gomes et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.2160.pdf