ComfyUI-FastMask

A simple, fast, custom-built mask editor for ComfyUI – an alternative to the built-in MaskEditor.

Installation

Method 1 – ComfyUI Manager (recommended)

1. Open ComfyUI Manager in ComfyUI (Manager menu → Custom Nodes Manager).
2. Search for fastmask
3. Click Install, then restart ComfyUI.

Method 2 – Git clone

cd ComfyUI/custom_nodes
git clone https://github.com/zaum/ComfyUI-FastMask

After restarting ComfyUI, look for the FastMask Editor node in the mask category.

Usage

1. Select an image in the node's image dropdown, upload one onto the node, or connect it to image_opt (a connected image overrides the dropdown).
2. Open the full-screen editor with Edit Mask, paint, then press OK.
3. The mask is saved at full resolution into ComfyUI/input/fastmask/ and restored on the next open. A composite preview (image + mask, max. 1024 px JPEG) is uploaded and shown permanently on the node.
4. Outputs: IMAGE (the loaded image) and MASK (1.0 = masked area).

Controls

Action	Command
Paint / Erase	Holdleft / right mouse button
Brush size	Ctrl + drag up/down, Ctrl + wheel, [ / ], or slider
Mask blur	Ctrl + drag left/right or the Blur slider (real-time preview in the B/W view)
Paint/Erase switch	X or the toggle
Zoom / Pan	Mouse wheel (cursor-anchored) / middle drag or hold Space
Closed-shape auto-fill	On by default – toggle:F
Undo / Redo	Ctrl+Z / Ctrl+Y or Ctrl+Shift+Z
Clear all	Ctrl+Delete or button
Show mask (B/W)	Hover the button for a preview, click to pin
Hatch color	C or the button
Fit image	Ctrl+0
OK / Cancel	Enter / Esc

Every button shows its shortcut on hover (mac: ⌘ instead of Ctrl).

Why is it fast?

• Dirty-rectangle rendering – each frame redraws only the touched areas, on a single requestAnimationFrame loop that sleeps when nothing changes.
• Native GPU canvas strokes – no per-stroke JS pixel copying; zoom/pan is a pure CSS transform (zero cost).
• Preview-resolution painting, full-res export – editing happens on a max. 2048 px preview; OK produces the mask at the full original resolution.
• Tile-based undo/redo – lazy 256×256 tile snapshots of only the touched tiles (max. 40 steps).
• Real-time mask blur (0–100%) and closed-shape evenodd fill; the node preview is a small pre-generated JPEG the frontend only displays.

Planned: in-browser SAM segmentation (MobileSAM/FastSAM via onnxruntime-web). Not implemented yet.

Compatibility

ComfyUI (latest frontend), Windows / Linux / macOS. Saving uses the standard /upload/image API – no extra server component.

License

MIT