Mask Batch to Mask

Some nodes hand you a batch of masks when you only want one. A segmenter that returns several candidate regions, a batch of frames each with its own mask, a multi-output masking step - you end up holding a MASK batch and the node downstream wants a single MASK. Mask Batch to Mask is the little adapter that fixes that: it returns one mask out of a batch, by index.

It's plumbing, plain and simple. But it's the kind of plumbing that unblocks a graph that would otherwise throw a shape error because a batch went somewhere a single mask was expected.

How it works

The README description is the whole thing: "Return a single mask from a batch of masks." You give it a mask batch and tell it which one you want (an index into the batch), and it pops that single mask out. Index 0 is the first mask, 1 the second, and so on.

This is the mask-world equivalent of grabbing one image out of an image batch. It doesn't combine or merge the masks - for that WAS has separate "combine" nodes - it just selects one.

Inputs and outputs that matter

The inputs are the MASK batch and the index of the one you want. The output is a single MASK, ready to feed an inpaint, a composite, or an Image Blend by Mask.

If your goal is the opposite - squashing several masks into one combined mask - this isn't it. Look at Masks Combine Masks or Masks Combine Batch in the same pack. Batch-to-Mask is strictly a pick one operation.

How to install it

ComfyUI Manager: search was-node-suite-comfyui, install, restart. Manually:

cd ComfyUI/custom_nodes
git clone https://github.com/WASasquatch/was-node-suite-comfyui

then install the pack's requirements.txt in your ComfyUI venv and restart. No downloads - it's tensor indexing.

Common issues & troubleshooting

I get the wrong mask / an out-of-range error. Indexing starts at 0. If your batch has four masks, valid indices are 0–3; asking for index 4 runs off the end. Count from zero.

It only ever returns one mask and I wanted to process all of them. By design - this node picks a single mask. If you need to run every mask in the batch through the same downstream logic, that's a batching/loop problem, not what this node solves. Either handle the batch as a batch downstream or select and process them one index at a time.

Select vs combine confusion. This selects one mask. If your composite looks wrong because you expected all the regions merged, you wanted a combine node instead. Batch-to-Mask throws away the masks you didn't pick.

The picked mask has holes or ragged edges. That's the mask's own quality, not the selection. Clean it after picking - Mask Fill Holes for interior gaps, smooth/dilate for edges - before you use it.

Whole pack won't import after a ComfyUI update. The recurring WAS Node Suite issue - package downgrades colliding with a ComfyUI bump. Re-run the pack's requirements against the activated venv, or install.bat. Maintenance-only since late 2023.