Center Image ♾️Mixlab

Mixlab has a whole subsystem built around a custom type called _GRID - a way of describing a rectangular region on a canvas that its own family of nodes (SplitImage, GridInput, GridOutput, GridDisplayAndSave) pass around and act on, mostly for regional-prompt layouts feeding GLIGEN. CenterImage is the manual, single-region entry point into that system: instead of automatically slicing a canvas into N even cells the way SplitImage does, you define exactly one region by how far it's inset from each edge.

How it works

You give it a canvas image and four margins - left, top, right, bottom - each in pixels. The node treats the canvas as a rectangle and shrinks it inward by those margins on each side, and that resulting inner rectangle becomes your region. It comes out as a _GRID (the same type the rest of the grid family trades in) plus a matching mask.

Think of it as marking "here's the middle bit I care about" on a template - a poster frame, a photo slot, the area you actually want to composite into - without doing pixel math yourself.

The inputs and outputs that matter

• canvas (IMAGE, required) - the image whose dimensions define the outer rectangle.
• left / top / right / bottom (INT, default 24 each, range 0–5000) - the margin to inset from each respective edge. Bigger numbers mean a smaller, more centered region.

Outputs: grid (_GRID) - the region descriptor, meant for sibling nodes like GridOutput (to turn it into real x/y/width/height) or GridDisplayAndSave (to preview and save it) - and mask, a plain mask of that same region for anything that just wants a MASK.

How to install it

Ships with the Mixlab pack.

• ComfyUI Manager: search comfyui-mixlab-nodes, install, restart.
• Manual: cd ComfyUI/custom_nodes && git clone https://github.com/shadowcz007/comfyui-mixlab-nodes.git, install requirements (install.bat on Windows, or ../../../python_embeded/python.exe -s -m pip install -r requirements.txt), restart.

No model downloads needed for this node specifically.

Common issues & troubleshooting

The region doesn't line up with what I expected. The margins are absolute pixels, not percentages - if you reuse the same CenterImage settings against a canvas of a different resolution, the region shifts relative to the image, since 24px means something very different on a 512px canvas versus a 4000px one. Match your margins to the actual canvas size you're working with, or recompute them if you change resolutions.

The grid output won't plug into anything. _GRID is Mixlab-specific - it only connects to the pack's own grid-aware nodes (GridOutput, GridDisplayAndSave, and GLIGEN's regional-apply node in this same pack), not generic image or crop nodes from elsewhere. If you need plain numbers, route the grid output through GridOutput first to get x/y/width/height.

I just want a rectangle mask, not the grid stuff. Use the mask output directly and ignore grid entirely - it's a completely valid way to use this node if all you want is "canvas minus a margin" as a mask for compositing or inpainting.