When I saw a certain Reddit thread, I was immediately inspired to test and create my own PIXART-Σ (PixArt-Sigma) ComfyUI workflow. The trick of this method is to use new SD3 ComfyUI nodes for loading t5xxl_fp8_e4m3fn.safetensors (5Gb - from the infamous SD3, instead of 20Gb - default from PixArt). And then refine the image (since Pixart does not support img2img = direct refinement) with SD15 model, which has low VRAM footprint. You can easily (if VRAM allows => 8Gb) convert this workflow to SDXL refinement by simply switching the loaded refiner model and the corresponding VAE to SDXL. (or just use attached workflow to this article for that - "PIXART E to SDXL")
1 - Install the "Extra Models For ComfyUI" package from Comfy Manager;
2 - Download PixArt-Sigma-XL-2-1024-MS.pth file from https://huggingface.co/PixArt-alpha/PixArt-Sigma/tree/main to your Comfy checkpoints folder;
3 - Download t5xxl_fp8_e4m3fn.safetensors file from https://huggingface.co/stabilityai/stable-diffusion-3-medium/tree/main/text_encoders to your Comfy Clip folder;
4 - Download some SD15 checkpoint (I'm using: https://civitai.com/models/338567/fantasyolives) to your Comfy checkpoints folder;
4.5 - Or, if your VRAM allows (even better) - use some SDXL checkpoint instead (I'm using: https://civitai.com/models/441242) as a refiner, but for that = switch final VAE loader to SDXL version. (ready-to-use workflow is in attachment)
5 - load the workflow from the attachment of this article into your ComfyUI ... happy generating!
Basically, in 5 easy steps now You can generate images with PIXART-Σ in ComfyUI, YAY!!!
kind of (6-ish) - if you do not want to use refiner at all - simply save image after the first VAE decoding to disk with corresponding node ...
For example:
SD15 refiner:
SDXL refiner:
For face/eyes you may want to add one more layer of refinement with FaceDetailer Comfyui node - but I'm NOT doing it here for simplicity of the workflow ... (it is in more complex workflow attached here as "PIXART E to SDXL FaceDetailer")
SDXL refiner + FaceDetailer node:
link to that last example: https://civitai.com/posts/3791707
Landscape example (SD15 refiner):
Landscape example (SDXL refiner):
Good Luck, Have Fun!!!
P.S.: Credit goes to the author of the initial workflow mentioned in Reddit thread above: https://www.reddit.com/user/ZootAllures9111/