Unifying Multimodal Retrieval via Document Screenshot Embedding
Authors: name: Xueguang Ma, name: Sheng-Chieh Lin, name: Minghan Li, name: Wenhu Chen, name: Jimmy Lin

In the real world, documents are organized in different formats and varied
modalities. Traditional retrieval pipelines require tailored document parsing
techniques and content extraction modules to prepare input for indexing. This
process is tedious, prone to errors, and has information loss. To this end, we
propose Document Screenshot Embedding} (DSE), a novel retrieval paradigm that
regards document screenshots as a unified input format, which does not require
any content extraction preprocess and preserves all the information in a
document (e.g., text, image and layout). DSE leverages a large vision-language
model to directly encode document screenshots into dense representations for
retrieval. To evaluate our method, we first craft the dataset of Wiki-SS, a
1.3M Wikipedia web page screenshots as the corpus to answer the questions from
the Natural Questions dataset. In such a text-intensive document retrieval
setting, DSE shows competitive effectiveness compared to other text retrieval
methods relying on parsing. For example, DSE outperforms BM25 by 17 points in
top-1 retrieval accuracy. Additionally, in a mixed-modality task of slide
retrieval, DSE significantly outperforms OCR text retrieval methods by over 15
points in nDCG@10. These experiments show that DSE is an effective document
retrieval paradigm for diverse types of documents. Model checkpoints, code, and
Wiki-SS collection will be released.