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Seeing vs reading: evaluating visual and textual approaches in retrieval-augmented generation

Plans Vilaseca, Júlia

UPCommons institutional repository (Universitat Politècnica de Catalunya), 2025

Abstract

This thesis presents a comparative analysis of visual and textual retrieval methods within Retrieval-Augmented Generation (RAG) systems, based on the hypothesis that visual models outperform textual ones in scenarios where visual resources are predominant. To validate this hypothesis, a rigorous experimentation process is conducted, starting with real data provided by a client, ensuring that the evaluated content was not used in any model training, thus offering a realistic evaluation context. As the need for broader experimentation arises, the study expands to include additional datasets such as TAT-DQA and NewsQA, and later the newly released Vidore V2 datasets-ensuring that these were not used in the training phase either. In total, ten datasets are analyzed using seven visual models and three textual models, with all models answering queries using the same context: images extracted through a visual processing pipeline and text obtained via Nuclia's processing system. Throughout the project, fairness in the comparison is strictly maintained, ensuring that the generative model receives equivalent contextual information in both modalities. The results show that there is no universally superior approach: performance depends on the type of query and the nature of the documents. In cases involving rich visual content (such as tables, graphs, or complex layouts), visual models generally perform better by leveraging this additional information. However, this advantage comes at a…

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