MIDR: Enrichment-Augmented Indexing for Multimodal Document Retrieval

Debanjan Mahata, Atharva Tendle, Daniel Preotiuc-Pietro, Yong Zhuang, Ozan Irsoy


Abstract
Retrieval over visually rich documents has a representation problem: important content often lives in tables, charts, figures, and layout relations that plain OCR linearizes, corrupts, or omits. ColPali-family visual retrievers address this with patch-level multi-vector indexes and late-interaction scoring, keeping image-derived retrieval on the query-time serving path. We introduce MIDR (Multimodal Indexing for Document Retrieval), a training-free framework for enrichment-augmented indexing that shifts multimodal reasoning to index time. During ingestion, a multimodal LLM converts rendered pages into verified textual fields that are indexed with BM25F and optionally fused with dense retrieval, enabling text-centric serving over multimodally grounded evidence. On ViDoRe V3, MIDR Hybrid achieves 0.6219 average nDCG across five English domains, a 23.0% relative gain over BM25, remaining competitive with ColQwen2.5. On two French-document domains, enrichment bridges English queries and French page text, lifting BM25 from 0.1532 to 0.5448 nDCG and outperforming ColQwen2.5. Across all seven domains, MIDR leads ColQwen2.5 on four while using ~9× smaller index memory and approximately 2× lower query latency. These results establish index-time multimodal reasoning as a compelling accuracy–deployment alternative to serving-time visual late interaction.
Anthology ID:
2026.emnlp-main.1731
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
39508–39530
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URL:
https://aclanthology.org/2026.emnlp-main.1731/
DOI:
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Cite (ACL):
Debanjan Mahata, Atharva Tendle, Daniel Preotiuc-Pietro, Yong Zhuang, and Ozan Irsoy. 2026. MIDR: Enrichment-Augmented Indexing for Multimodal Document Retrieval. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 39508–39530, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
MIDR: Enrichment-Augmented Indexing for Multimodal Document Retrieval (Mahata et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1731.pdf