Ghostwritten Studios — BiRefNet Background Removal

A self-contained ComfyUI custom node for BiRefNet background removal. It does not depend on any other third-party ComfyUI extension, so a ComfyUI update can't silently break the app that relies on it. The only external piece is the model weights, pulled once from Hugging Face and cached locally.

Nodes

Node	Category	Purpose
Ghostwritten Remove Background	Ghostwritten Studios	IMAGE → RGBA IMAGE + MASK. Loads the model itself if no loader is connected.
Ghostwritten BiRefNet Loader	Ghostwritten Studios	(Optional) Load a model once and reuse the handle across multiple nodes.

Outputs

• rgba_image (IMAGE) — 4-channel RGBA. Feed straight into a Save Image node to get a transparent PNG (ComfyUI's SaveImage writes the alpha channel).
• mask (MASK) — raw foreground matte, 0–1.

Options (Remove Background)

• model_name — BiRefNet (general), BiRefNet_lite (faster), BiRefNet-portrait, BiRefNet HR (1536).
• precision — fp16 (default, CUDA) or fp32.
• mask_blur — feather the matte edge (px).
• mask_offset — grow (+) / shrink (−) the matte (px).
• invert_mask — keep the background instead of the subject.

Model weights

Downloaded automatically on first use via transformers + trust_remote_code=True, cached under ~/.cache/huggingface. Repos:

• ZhengPeng7/BiRefNet · ZhengPeng7/BiRefNet_lite
• ZhengPeng7/BiRefNet-portrait · ZhengPeng7/BiRefNet_HR

Requires timm, einops, kornia (already present in this ComfyUI install).

Minimal API workflow (single node)

{
  "10": { "class_type": "LoadImage", "inputs": { "image": "input.png" } },
  "11": { "class_type": "GhostwrittenRemoveBackground",
          "inputs": { "image": ["10", 0], "model_name": "BiRefNet (general)",
                      "precision": "fp16", "mask_blur": 0, "mask_offset": 0,
                      "invert_mask": false } },
  "12": { "class_type": "SaveImage",
          "inputs": { "filename_prefix": "GhostwrittenStudios_cutout",
                      "images": ["11", 0] } }
}

Restart ComfyUI after installing so the nodes register.