# FreeU

[FreeU](https://huggingface.co/papers/2309.11497) improves image detail by rebalancing how much the UNet decoder draws from backbone features versus skip-connection features. Skip connections can drown out the backbone's semantic features, which produces unnatural detail in the output. FreeU needs no training, and you can turn it on or off at inference time for text-to-image and text-to-video pipelines.

> [!NOTE]
> FreeU only works with UNet-based pipelines like Stable Diffusion, SDXL, and AnimateDiff. It isn't supported by transformer-based pipelines like Flux or Qwen-Image.

Use the [enable_freeu()](/docs/diffusers/main/en/api/pipelines/overview#diffusers.StableDiffusionMixin.enable_freeu) method on your pipeline and configure the scaling factors. `b1` and `b2` amplify the backbone features, and `s1` and `s2` dampen the skip features. The `1` and `2` refer to the first two upsampling stages of the UNet decoder. See the [FreeU](https://github.com/ChenyangSi/FreeU#parameters) repository for reference hyperparameters for different models.

Start with the repository values for a model. To tune for other models, keep `s1=0.9` and `s2=0.2` and adjust `b1` and `b2` first. Setting all four factors to `1.0` is the same as disabling FreeU. Larger `b` values strengthen the effect but can oversmooth fine texture, and lowering `s1` and `s2` counteracts that.

```py
import torch
from diffusers import DiffusionPipeline

pipeline = DiffusionPipeline.from_pretrained(
    "stabilityai/stable-diffusion-xl-base-1.0", dtype=torch.float16,
).to("cuda")  # or "mps", "xpu", "cpu"
pipeline.enable_freeu(s1=0.9, s2=0.2, b1=1.3, b2=1.4)
generator = torch.Generator(device="cpu").manual_seed(13)
prompt = "A squirrel eating a burger"
image = pipeline(prompt, generator=generator).images[0]
image
```

  
    
    FreeU disabled
  
  
    
    FreeU enabled
  

Call the [disable_freeu()](/docs/diffusers/main/en/api/pipelines/overview#diffusers.StableDiffusionMixin.disable_freeu) method to disable FreeU.

```py
pipeline.disable_freeu()
```

## Next steps

- See the [enable_freeu()](/docs/diffusers/main/en/api/pipelines/overview#diffusers.StableDiffusionMixin.enable_freeu) API reference for the full parameter descriptions.
- Try FreeU on video with [AnimateDiff](../api/pipelines/animatediff).