Scaling Language-Centric Omnimodal Representation Learning
Authors: name: Chenghao Xiao; name: Hou Pong Chan; name: Hao Zhang; name: Weiwen Xu; name: Mahani Aljunied; name: Yu Rong
Published: 2025-10-13 17:53:52

Abstract: Recent multimodal embedding approaches leveraging multimodal large language
models (MLLMs) fine-tuned with contrastive learning (CL) have shown promising
results, yet the underlying reasons behind their superiority remain
underexplored. This work argues that a crucial advantage of MLLM-based
approaches stems from implicit cross-modal alignment achieved during generative
pretraining, where the language decoder learns to exploit multimodal signals
within a shared representation space for generating unimodal outputs. Through
analysis of anisotropy and kernel similarity structure, we empirically confirm
that latent alignment emerges within MLLM representations, allowing CL to serve
as a lightweight refinement stage. Leveraging this insight, we propose a
Language-Centric Omnimodal Embedding framework, termed LCO-Emb. Extensive
experiments across diverse backbones and benchmarks demonstrate its
effectiveness, achieving state-of-the-art performance across modalities.
Furthermore, we identify a Generation-Representation Scaling Law (GRSL),
showing that the representational capabilities gained through contrastive
refinement scales positively with the MLLM's generative capabilities. This
suggests that improving generative abilities evolves as an effective paradigm
for enhancing representation quality. We provide a theoretical explanation of
GRSL, which formally links the MLLM's generative quality to the upper bound on
its representation performance, and validate it on a challenging, low-resource
visual-document retrieval task, showing that continual generative pretraining
before CL can further enhance the potential of a model's embedding
capabilities. Codes, models, and resources are available at
https://github.com/LCO-Embedding/LCO-Embedding.