Finite Difference Flow Optimization for RL Post-Training of Text-to-Image Models

Fuente: arXiv
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Autores principales: McAllister, David, Aittala, Miika, Karras, Tero, Hellsten, Janne, Kanazawa, Angjoo, Aila, Timo, Laine, Samuli
Formato: Preprint
Publicado: 2026
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author McAllister, David
Aittala, Miika
Karras, Tero
Hellsten, Janne
Kanazawa, Angjoo
Aila, Timo
Laine, Samuli
author_facet McAllister, David
Aittala, Miika
Karras, Tero
Hellsten, Janne
Kanazawa, Angjoo
Aila, Timo
Laine, Samuli
contents Reinforcement learning (RL) has become a standard technique for post-training diffusion-based image synthesis models, as it enables learning from reward signals to explicitly improve desirable aspects such as image quality and prompt alignment. In this paper, we propose an online RL variant that reduces the variance in the model updates by sampling paired trajectories and pulling the flow velocity in the direction of the more favorable image. Unlike existing methods that treat each sampling step as a separate policy action, we consider the entire sampling process as a single action. We experiment with both high-quality vision language models and off-the-shelf quality metrics for rewards, and evaluate the outputs using a broad set of metrics. Our method converges faster and yields higher output quality and prompt alignment than previous approaches.
format Preprint
id arxiv_https___arxiv_org_abs_2603_12893
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Finite Difference Flow Optimization for RL Post-Training of Text-to-Image Models
McAllister, David
Aittala, Miika
Karras, Tero
Hellsten, Janne
Kanazawa, Angjoo
Aila, Timo
Laine, Samuli
Computer Vision and Pattern Recognition
Artificial Intelligence
Machine Learning
Neural and Evolutionary Computing
Reinforcement learning (RL) has become a standard technique for post-training diffusion-based image synthesis models, as it enables learning from reward signals to explicitly improve desirable aspects such as image quality and prompt alignment. In this paper, we propose an online RL variant that reduces the variance in the model updates by sampling paired trajectories and pulling the flow velocity in the direction of the more favorable image. Unlike existing methods that treat each sampling step as a separate policy action, we consider the entire sampling process as a single action. We experiment with both high-quality vision language models and off-the-shelf quality metrics for rewards, and evaluate the outputs using a broad set of metrics. Our method converges faster and yields higher output quality and prompt alignment than previous approaches.
title Finite Difference Flow Optimization for RL Post-Training of Text-to-Image Models
topic Computer Vision and Pattern Recognition
Artificial Intelligence
Machine Learning
Neural and Evolutionary Computing
url https://arxiv.org/abs/2603.12893