UniFusion: Vision-Language Model as Unified Encoder in Image Generation
Authors: name: Kevin Li; name: Manuel Brack; name: Sudeep Katakol; name: Hareesh Ravi; name: Ajinkya Kale
Published: 2025-10-14 17:57:56

Abstract: Although recent advances in visual generation have been remarkable, most
existing architectures still depend on distinct encoders for images and text.
This separation constrains diffusion models' ability to perform cross-modal
reasoning and knowledge transfer. Prior attempts to bridge this gap often use
the last layer information from VLM, employ multiple visual encoders, or train
large unified models jointly for text and image generation, which demands
substantial computational resources and large-scale data, limiting its
accessibility.We present UniFusion, a diffusion-based generative model
conditioned on a frozen large vision-language model (VLM) that serves as a
unified multimodal encoder. At the core of UniFusion is the Layerwise Attention
Pooling (LAP) mechanism that extracts both high level semantics and low level
details from text and visual tokens of a frozen VLM to condition a diffusion
generative model. We demonstrate that LAP outperforms other shallow fusion
architectures on text-image alignment for generation and faithful transfer of
visual information from VLM to the diffusion model which is key for editing. We
propose VLM-Enabled Rewriting Injection with Flexibile Inference (VERIFI),
which conditions a diffusion transformer (DiT) only on the text tokens
generated by the VLM during in-model prompt rewriting. VERIFI combines the
alignment of the conditioning distribution with the VLM's reasoning
capabilities for increased capabilities and flexibility at inference. In
addition, finetuning on editing task not only improves text-image alignment for
generation, indicative of cross-modality knowledge transfer, but also exhibits
tremendous generalization capabilities. Our model when trained on single image
editing, zero-shot generalizes to multiple image references further motivating
the unified encoder design of UniFusion.