Multi-Resolution Flow Matching: Training-Free Diffusion Acceleration via Staged Sampling
arXiv · HuggingFace · ▲32
Abstract (verbatim)
Hardware-agnostic strategies for accelerating text-to-image diffusion, such as timestep distillation and feature caching, can reduce inference time without custom kernels or system-level optimization. Among them, multi-resolution generation strategies have recently received broad attention, attaining more than 5x speedup without any training. However, the design of performing upsampling in the latent space, together with the selective modification of partial regions, causes these methods to exhibit noticeable blurring or artifacts. To this end, we propose MrFlow, a training-free multi-resolution acceleration strategy for pretrained flow-matching models built upon a staged low-to-high-resolution pipeline. MrFlow first rapidly generates the main structure at low resolution, then performs super-resolution in the pixel space using a lightweight pretrained GAN-based model, subsequently injects low-strength noise to enable high-frequency resampling, and finally refines the details at high resolution. Quantitative and qualitative results on FLUX.1-dev and Qwen-Image show that MrFlow exploits the quadratic token reduction and reduced step requirement of low-resolution sampling to achieve 10x end-to-end acceleration while keeping OneIG within a 1% gap relative to that before acceleration, significantly surpassing other training-free acceleration strategies, and requiring no training or runtime dynamic identification whatsoever. MrFlow can further be directly combined orthogonally with pre-trained timestep distillation strategies, achieving even higher generation acceleration of up to 25x.
Background
Background Analysis
1. Technical Context
Recent advances in image generation using diffusion models (e.g., Transformer-based architectures or flow matching paradigms) have improved quality but at the cost of increasing computational demands. For instance, large models like Qwen-Image-20B may require hundreds of sampling steps for a single text-to-image task, leading to long inference times. This inefficiency limits real-world applications (e.g., real-time interactions or resource-constrained devices). Researchers thus seek acceleration methods that reduce computation without compromising quality.
2. Previous Limitations
Existing acceleration strategies face challenges:
- Training or system dependency: Methods like timestep distillation require retraining, while feature caching relies on system-level optimizations, limiting generality.
- Limited speedup: Most approaches achieve only 2-5x faster inference and may introduce blurring or artifacts.
- Multi-resolution drawbacks: While low-resolution generation followed by high-resolution refinement (e.g., latent upsampling) can boost speed, latent upsampling often causes structural distortions, and dynamic region identification adds complexity.
3. Proposed Solution
This paper introduces MrFlow, a training-free multi-resolution acceleration strategy based on a coarse-to-fine staged pipeline:
1. Low-resolution generation: A pretrained diffusion model quickly generates the image structure at low resolution, reducing computation and steps.
2. Pixel-space super-resolution: A lightweight GAN-based network upscales the image in pixel space, preserving structure while adding high-frequency details.
3. Noise injection and high-resolution refinement: Weak noise is injected to correct errors from super-resolution, followed by high-resolution sampling to refine details.
This approach avoids latent-space artifacts and leverages spatial properties (e.g., clear structures at low resolution, rich details at high resolution) for efficiency.
4. Key Differences
Compared to prior work, MrFlow stands out by:
- No training or dynamic identification: It works directly with pretrained models, simplifying deployment.
- Staged design: It clearly separates structure generation, super-resolution, and refinement, reducing complexity.
- Compatibility: It can be combined orthogonally with existing methods (e.g., timestep distillation) for up to 25x faster inference.
By balancing quality and speed, MrFlow achieves over 10x end-to-end acceleration without sacrificing performance.




