Fill Dark Mask

Let's be upfront about this one: it's the least documented node in an already lightly-documented pack. ComfyUI-fastblend's README walks through SmoothVideo, InterpolateKeyFrame, reBatchImage and MyOpenPoseNode by name, then closes that section with "other nodes don't have much use, so I'm not going to introduce [them]." FillDarkMask is one of those other nodes - it exists, it loads, but the author never explains what it's for beyond what you can infer from the name and the node's own inputs and outputs.

Here's what's actually verifiable: it takes a MASK in and returns a MASK out, with zero configurable parameters - no threshold, no mode switch, nothing to tune. Given the name, the reasonable read is that it's doing exactly what it says: filling gaps or holes in a mask, likely small dark/zero regions that show up when a mask comes out of something like a SAM detector or a depth-based cutout with tiny pinholes in it. That's an inference from the name and the I/O shape, not a confirmed mechanism - there's no source walkthrough or tooltip to point to, and I'd rather tell you that plainly than invent a threshold parameter that doesn't exist in the schema.

The inputs and outputs that matter

There genuinely isn't much here, which is itself the point:

• masks (MASK) - your input mask, or mask batch.
• Output: MASK - presumably the same mask with dark/empty regions filled, though whether that's a simple flood-fill, a morphological close, or something more specific to the author's own video2video workflow isn't documented anywhere in the pack.

No widgets, no options, nothing else to configure. If you were expecting a fill threshold or a mode toggle, it isn't there.

How to install it

It ships in the same pack as everything else here, so if you've already installed ComfyUI-fastblend for FastBlend or MyOpenPoseNode, you already have this node too. Via ComfyUI Manager: search "ComfyUI-fastblend," install, restart. Manually:

cd ComfyUI/custom_nodes
git clone https://github.com/AInseven/ComfyUI-fastblend

Restart ComfyUI. No models, no extra dependencies beyond the pack itself.

Common issues & troubleshooting

You can't tell if it's doing anything. Given the total lack of documentation, the most useful thing you can do is A/B it: run your mask pipeline with and without this node in the chain and diff the two results. With no threshold to adjust and no tooltip to lean on, empirical comparison is genuinely the fastest way to understand its actual effect on your specific mask.

Output looks identical to input. If your source mask doesn't have dark gaps to begin with, there may be nothing visible for this node to change - that would be consistent with a gap-filling operation that's a no-op on an already-clean mask.

You need to know exactly what it does. Given the pack is a small, actively-maintained personal repo, the fastest path to a real answer is opening an issue on the GitHub repo directly and asking - small one-author packs like this tend to get a straight answer faster than digging through undocumented source.