sd-perturbed-attention/README.md

Perturbed-Attention Guidance for ComfyUI / SD WebUI (Forge)

Implementation of Self-Rectifying Diffusion Sampling with Perturbed-Attention Guidance (D. Ahn et al.) as an extension for ComfyUI and SD WebUI (Forge).

Works with SD1.5 and SDXL.

Doesn't work with Stable Cascade.

PAG may produce striped "noise", setting sigma_end to 0.7 or higher may reduce striped patterns.

Paper and demo suggest using CFG scale 4.0 with PAG scale 3.0 applied to U-Net's middle layer 0, but feel free to experiment.

Sampling speed without adaptive_scale or sigma_start / sigma_end is similar to Self-Attention Guidance (x0.6 of usual it/s).

Installation

ComfyUI

Basic PAG node is now included into ComfyUI - you don't have to install this extension unless you want to mess with additional parameters.

To install the advanced PAG node from this repo, you can either:

• git clone https://github.com/pamparamm/sd-perturbed-attention.git into ComfyUI/custom-nodes/ folder.

• Install it via ComfyUI Manager (search for custom node named "Perturbed-Attention Guidance").

• Install it via comfy-cli with comfy node registry-install sd-perturbed-attention

SD WebUI (Forge)

git clone https://github.com/pamparamm/sd-perturbed-attention.git into stable-diffusion-webui-forge/extensions/ folder.

You can override CFG Scale and PAG Scale for Hires. fix by opening/enabling Override for Hires. fix tab. To disable PAG during Hires. fix, set PAG Scale under Override to 0.

SD WebUI (Auto1111)

As an alternative for A1111 WebUI you can use PAG implementation from sd-webui-incantations extension.

Parameters

• scale: PAG scale, has some resemblance to CFG scale - higher values can both increase structural coherence of the image and oversaturate/fry it entirely.
• adaptive_scale: PAG dampening factor, it penalizes PAG during late denoising stages, resulting in overall speedup: 0.0 means no penalty and 1.0 completely removes PAG.
• unet_block: Part of U-Net to which PAG is applied, original paper suggests to use middle.
• unet_block_id: Id of U-Net layer in a selected block to which PAG is applied. PAG can be applied only to layers containing Self-attention blocks.
• sigma_start / sigma_end: PAG will be active only between sigma_start and sigma_end. Set both values to negative to disable this feature.
• rescale_pag: Acts similar to RescaleCFG node - it prevents over-exposure on high scale values. Based on Algorithm 2 from Common Diffusion Noise Schedules and Sample Steps are Flawed (Lin et al.). Set to 0 to disable this feature.
• rescale_mode:
  • full - takes into account both CFG and PAG.
  • partial - depends only on PAG.
• unet_block_list: Replaces both unet_block and unet_block_id, allows you to select multiple U-Net layers separated with commas. SDXL U-Net has multiple indices for layers, you can specify them using dot symbol (if not specified, PAG would be applied to the whole layer). Example value: m0,u0.4 (PAG will be applied to middle block 0 and to output block 0 with index 4)
  • d means input, m means middle and u means output.
  • SD1.5 U-Net has layers d0-d5, m0, u0-u8.
  • SDXL U-Net has layers d0-d3, m0, u0-u5. In addition, each block except d0 and d1 has 0-9 index values (like m0.7 or u0.4). d0 and d1 have 0-1 index values.

ComfyUI TensorRT

To use PAG together with ComfyUI_TensorRT, you'll need to:

1. Build static/dynamic TRT engine of a desired model.
2. Build static/dynamic TRT engine of the same model with the same TRT parameters, but with fixed PAG injection in selected UNET blocks (TensorRT Attach PAG node).
3. Use TensorRT Perturbed-Attention Guidance node with two model inputs: one for base engine and one for PAG engine.