Mask

Mask is the rare node in the ComfyUI-CUP pack that actually does something useful on its own, with no Blender in sight: it takes an image file and extracts a single channel - alpha, red, green, or blue - as a ComfyUI MASK tensor. Simple, boring, and genuinely handy.

Channel-to-mask extraction is a workhorse trick in image pipelines. Selection masks stored in an image's alpha channel, mattes hidden in a green channel, channel-packed data (the classic way to stash a mask inside an RGB image) - Mask lets you pull any of those out and use it to drive inpainting, compositing, or conditioning. If you've ever had a workflow that expected a MASK but you only had an image file, this node is the missing adapter.

How it works

• image (STRING) - a path to the image file on disk. Not a tensor input; it opens the file directly.
• channel (enum) - which channel to extract: alpha, red, green, or blue.

Output: a single MASK tensor, normalized to 0–1. One detail worth knowing: the alpha channel comes out inverted (1 - alpha), so that opaque areas - which have alpha = 1 - become mask value 0, matching ComfyUI's convention where white (1) means "this region is masked/interpolated." The RGB channels come out as-is.

Like most of CUP, it's forgiving to the point of being dangerous: if the file doesn't exist, or the requested channel isn't in the image's bands (asking for red on a grayscale PNG, for example), you don't get an error - you get a 64×64 mask of zeros. Fine for a graceful fallback, maddening when you're debugging why a mask silently does nothing.

Install

Ships with ComfyUI-CUP. ComfyUI Manager → search ComfyUI-CUP, or:

cd ComfyUI/custom_nodes
git clone https://github.com/AIGODLIKE/ComfyUI-CUP.git

Restart after. No extra dependencies or model files.

The honest assessment

Unlike the OpenPose loaders in this pack, Mask isn't glued to the Blender bridge - it works in a plain web workflow the moment you give it a file path. It's a genuinely useful little utility, the kind you'll add to a few workflows and forget you have. Just don't feed it a directory or a nonexistent path expecting an error message to guide you; the pack's design philosophy is "return zeros and move on."