ComfyUI Outpaint Mask

Custom ComfyUI node for creating outpaint masks interactively.

Select or upload an image on the node (or hover the preview and use the clipboard-paste icon).

• 8 draggable handles: corners resize proportionally by default (hold Shift for free resize)
• Snapping to the original image edges and to 16 px multiples.
• Aspect-ratio preset buttons (1:1, 3:2, 2:3, 4:3, 3:4, 16:9, 9:16, 21:9, 9:21)
• Pixel/millimeter readout switch (px | mm) with a DPI field.
• Adjustable megapixel cap ("Limit megapixel" toggle + slider with typical values + narrow manual input) that the frame area cannot exceed. Slider stops track native model sizes.

The node outputs:

• cropped_image — the frame canvas = your render tile (size and context drawn by hand, it may cut into the source), empty outpaint areas are mid-gray (128).
• cropped_mask — 1.0 where the image must be generated (outside the original, inside the frame), 0.0 over the original image.
• original_image — FULL canvas (whole source + outpaint expansion, nothing cropped away): the source on mid-gray.
• original_mask — full-canvas mask: 0.0 over the source and 1.0 in the outpaint area.
• crop_x / crop_y — top-left position of the tile on the full canvas. These outputs enable compositing the generated tile back into original_image.

Compositing: Flux2 Klein example

If we not only want to use outpainting but have also cropped a high-resolution image, we can reinsert the cropped section back into the original image. The basic method is use the Composite node.

See the Flux2 Klein sample workflow

Install

Recommended: install with the ComfyUI extension manager. Open Manager → Custom Nodes Manager, search for ComfyUI-OutpaintMask (author: zaum), click Install, and restart ComfyUI.

Manual install: copy (or symlink) this folder into ComfyUI/custom_nodes/ComfyUI-OutpaintMask and restart ComfyUI. No extra Python dependencies beyond the ComfyUI core.