Invert Mask Regions

The simplest node in this entire filter family, and one of the most-used mask operations in any ComfyUI graph: SaltMaskInvert flips a mask so what was selected becomes unselected and vice versa. A "select the subject" mask becomes a "select the background" mask in one node. If you've built more than a couple of masking workflows, you've needed this - a segmentation model gives you the foreground, but your actual next step needs the background, or you generated a mask meant for "protect this area" when the node downstream expects "affect this area."

How it works

There's no cleverness to explain - it's arithmetic inversion. Every pixel value in the mask gets replaced with its complement: what was fully "on" becomes fully "off," what was fully "off" becomes fully "on," and anything in between (soft, partially-transparent edges) gets mirrored around the midpoint rather than snapped to a hard value. A feathered edge stays feathered after inversion; it just points the other way.

The inputs and outputs that matter

• masks (required, MASK) - that's the whole input list. Nothing to configure.

Output: MASKS, the complement of what went in.

How to install it

SaltMaskInvert is part of get-salt-AI/SaltAI, published as "SaltAI-Open-Resources" by Salt AI (getsalt.ai). The company launched in March 2024 to run ComfyUI workflows as hosted Discord bots and later an API; this masking node family - along with a set of animation-scheduling nodes that take FLOAT/INT lists - was the general-purpose utility layer in the same repo, useful independent of the platform itself.

Worth knowing up front if you go looking: github.com/get-salt-AI/SaltAI currently 404s. The org page is still live with a few other repos, but this one isn't listed anymore, and it's also absent from ComfyUI Manager's node index - so neither a Manager search nor a fresh git clone will currently turn it up. That said, if this specific node is all you need, it's about as replaceable as a custom node gets: basic mask inversion is one line of code (1.0 - mask), and if you're blocked on getting SaltAI itself, most general-purpose mask packs (Impact Pack, WAS Node Suite, and others already common in a typical install) ship an equivalent invert node. If SaltAI is already in your environment, though, there's nothing else to worry about here - no model downloads, no dependency on Salt AI's own servers.

Common issues & troubleshooting

Your composite came out backwards. This is the single most common mask bug in any ComfyUI graph, and it usually isn't this node's fault - it's an invert applied at the wrong point, or one too many/too few inversions somewhere upstream. Trace the mask through your graph with a Preview Image node at each step until you find where "affect this" flipped to "protect this."

A soft-edged mask looks the same after inverting, just less obviously. Because inversion mirrors values rather than snapping them, a feathered mask stays feathered - you won't get a hard edge just because you inverted it. If you need a crisp boundary, that's a separate step (thresholding), not something inversion gives you as a side effect.

Double-inverting and wondering why nothing changed. Two inverts cancel out, which is correct behavior, not a bug - if a mask looks unchanged after passing through what you thought was one SaltMaskInvert, check whether it actually went through two somewhere in the graph.

You need to invert only part of a multi-region mask, not the whole thing. This node operates on the entire mask uniformly - it has no concept of "these regions only." If you need selective inversion, split the mask into regions first with SaltMaskRegionSplit, invert the specific output you care about, then recombine.