BMAB Outpaint By Ratio

Most of BMAB's resize and detail nodes need a bind from an Integrator node upstream. This one doesn't - it just takes an image and a prompt, and does the whole outpainting job itself: extend the canvas, generate new content in the border, iterate until the seam settles. That standalone design makes it the simplest way to extend an image inside BMAB without building out a full pipeline first.

What ratio actually means here

ratio (0.1-0.95, default 0.85) is the fraction of the new, larger canvas that your original image occupies - not how much bigger the canvas gets. At the default 0.85, your original image fills 85% of the final frame and the remaining 15% is new, generated content. Push it down toward 0.1 for a dramatic extension where your original becomes a small fraction of a much bigger scene; keep it up near 0.9 for a subtle nudge outward.

alignment picks where your original sits within that bigger frame - center, or one of eight edge/corner positions - the same set of options BMAB Zoom Out uses. Off-center alignment is how you extend mostly in one direction (reveal more of what's to the left, say) instead of symmetrically in all directions.

Why iteration is the interesting field

iteration (1-8, default 4) runs the outpaint fill across multiple passes instead of one shot. This matches a real, well-established pattern for canvas extension: a single aggressive fill pass tends to leave a visible "pasted on" seam, while several smaller passes - generous overlap with the original, blending in gradually - read as continuous. Defaulting to 4 rather than 1 means BMAB is already doing the multi-pass thing the hard way for you, rather than leaving it as tuning advice you'd have to discover yourself.

The rest of the inputs

• steps (default 8) - notably lower than the 20-step default you'll see on BMAB's sampler-driven nodes, since this runs per iteration and the iterations compound.
• dilation (default 32) - how far the generated fill blends at the boundary with the original pixels.
• prompt - describes what should appear in the newly generated area. Leaving this vague (or empty) tends to produce more generic, less coherent extensions; describing the scene you actually want out there matters more here than in most BMAB nodes.

There's no bind, no cfg_scale, no sampler_name, no denoise exposed - this node handles its own sampling internally rather than inheriting settings from an upstream Integrator, which is the trade-off for not needing one. Output is a single image; no bind comes back out, so if you want to keep chaining into other BMAB pipeline nodes afterward, you'll need to feed this node's output image into a fresh Integrator.

Installing it

ComfyUI Manager: search comfyui_bmab, install, restart. By hand:

cd ComfyUI/custom_nodes
git clone https://github.com/portu-sim/comfyui_bmab.git
cd comfyui_bmab
pip install -r requirements.txt

plus comfyui_controlnet_aux and ComfyUI_IPAdapter_plus, the two companion packs the README asks for alongside comfyui_bmab regardless of the specific node.

Where this trips people up

The biggest one is confusing ratio for a growth factor the way BMAB Zoom Out's ratio works - they're not the same measurement. Zoom Out's ratio is how much bigger the new canvas is; this node's ratio is what fraction of the new canvas your original still occupies. Setting this one to 1.25 expecting a modest extension (borrowing Zoom Out's mental model) will error or clamp, since it only accepts values up to 0.95. The other miss is an empty or generic prompt on a big extension - with ratio pushed low and a lot of new canvas to fill, a vague prompt gives the model too little to work with and the extension tends to drift into something unrelated to the original scene.