StitchByMask

StitchByMask blends a foreground and background image using a mask with optional feathering and opacity control. It’s the quick way to composite retouched faces, outfit swaps, or background replacements inside ComfyUI.

Inputs

foreground – Image that should appear wherever the mask is white.
background – Image that fills in when the mask is black. Use the same resolution as the foreground.
mask – Greyscale mask controlling the blend. White reveals the foreground, black reveals the background.
invert_mask – Flip mask interpretation without editing the mask itself.
feather_px – Apply additional smoothing to the mask edge in pixels.
opacity – Blend strength from 0.0 (only background) to 1.0 (full foreground).
preserve_metadata – Pass through metadata from the foreground when True; otherwise copy from the background.

Outputs

image – Composited result.
mask – The mask after any feathering or inversion (useful for debugging or saving).

Where It Fits

Use StitchByMask when weaving together portrait fixes: slipping a cleaned-up face back into the original plate, combining outfit variations, or dropping a new background behind a subject. It also pairs with outpaint padding to smooth transitions.

Tuning Tips

Keep opacity just under 1.0 (e.g., 0.95) to allow subtle bleed from the background and avoid hard seams.
Apply feathering sparingly; you can always stack another blur if the edge still feels sharp.
Invert the mask via invert_mask rather than regenerating the mask upstream—fewer steps, same result.

Troubleshooting

Harsh seam visible – Increase feather_px slightly or ensure the mask resolution matches the images exactly.
Blend looks washed out – Check opacity; if it’s below 1.0, the background will bleed through more strongly.
Wrong area reveals – Flip invert_mask or verify the mask isn’t inverted before it reaches the node.

Screenshot: docs/screenshots/stitch_by_mask.png

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