Text, Pixels, or Both? Evaluating Input Representations for Multimodal Document QA

Nikhil Reddy Pottanigari, Sepideh Kharaghani, Saverio Vadacchino, Alejandro Posada, Kurt MacDonald, Ying Zhang


Abstract
Every document QA system begins with a choice that is rarely studied on its own: whether to feed the model page images, extracted text, or both. We isolate this choice, holding the prompt, judge, and scoring pipeline fixed, across four commercial model endpoints, two corpora, and two context regimes (gold evidence pages and the full document). On documents that fit the image budget, page images lead on accuracy at every document length on both corpora, but this advantage carries a growing latency and cost premium: text latency stays roughly flat as documents lengthen while image latency rises steadily. Text and images also fail on different questions, with exactly one representation correct on 19-25% of items across the reported cells, so neither subsumes the other. Exploiting this complementarity, a lightweight TF-IDF router that reads only the question text gains 2.6 points over always-text while cutting median latency 30% relative to always-vision, on a document-disjoint held-out split.
Anthology ID:
2026.docinsights-1.4
Volume:
The Proceedings of Workshop on Document Intelligence and Understanding
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Santosh T.Y.S.S., Amit Agarwal, Vivek Gupta, Yova Kementchedjhieva, Aparna Garimella, Yufang Hou
Venues:
DocInsights | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
46–62
Language:
URL:
https://aclanthology.org/2026.docinsights-1.4/
DOI:
Bibkey:
Cite (ACL):
Nikhil Reddy Pottanigari, Sepideh Kharaghani, Saverio Vadacchino, Alejandro Posada, Kurt MacDonald, and Ying Zhang. 2026. Text, Pixels, or Both? Evaluating Input Representations for Multimodal Document QA. In The Proceedings of Workshop on Document Intelligence and Understanding, pages 46–62, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Text, Pixels, or Both? Evaluating Input Representations for Multimodal Document QA (Pottanigari et al., DocInsights 2026)
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PDF:
https://aclanthology.org/2026.docinsights-1.4.pdf