AlphaChanelAdd

AlphaChanelAdd appends a fully opaque alpha channel to an RGB image, turning a 3-channel IMAGE tensor into a 4-channel RGBA one. That's the entire job, and yes, the name is misspelled ("Chanel", one L) - it's a family-wide typo in this pack, so if your search for "AlphaChannel" finds nothing, you're not crazy; it's spelled AlphaChanel.

Why would you want an alpha channel on a photo that has no transparency? Because a growing number of ComfyUI operations expect or tolerate RGBA, and mixing channel counts silently breaks downstream nodes. If you're about to composite two images, run an alpha-based operation, or save a PNG that should carry transparency metadata, having the alpha channel present before it's needed saves you a class of confusing "channel mismatch" errors. This node is the canonical fix: no alpha → opaque alpha, done.

The mechanism is as plain as the name: it checks the tensor's channel count, and if it's already 4 it returns the image untouched (idempotent - safe to run twice). Otherwise it appends an all-ones alpha layer, meaning the whole image is fully opaque. There are no parameters at all - one images input, one IMAGE output. It works across the whole batch and preserves your existing RGB channels byte-for-byte.

It's part of a small family in the Allor pack: AlphaChanelAddByMask (build alpha from a mask), AlphaChanelAsMask (pull alpha out as a mask), AlphaChanelRemove (drop alpha), and AlphaChanelRestore (reset a damaged alpha to opaque). Together they're the plumbing you reach for when cutting out subjects or prepping for compositing. A typical flow: ImageSegmentation produces an RGBA cutout → AlphaChanelRemove if a consumer insists on RGB → or AlphaChanelAsMask to reuse the transparency as a mask.

Installing it

It ships with the Allor plugin:

cd ComfyUI/custom_nodes
git clone https://github.com/Nourepide/ComfyUI-Allor
cd ComfyUI-Allor
pip install -r requirements.txt

Restart ComfyUI, or search "Allor" in ComfyUI Manager. Pack-level notes: requirements.txt installs rembg and onnx for the segmentation nodes even though this node is pure tensor math, and Allor's repo was rebased to strip images from git history (a ~344x size cut) - auto-update failures are a known side effect, and the docs at nourepide.github.io/ComfyUI-Allor-Doc have troubleshooting pages for them.

Real talk

This is a "fix my tensor shape" utility, and it's genuinely the right tool when channel-count errors are stalking your graph. Just don't expect it to create transparency out of nowhere - opaque alpha is opaque, which is the point. And while you're here, get used to the Chanel spelling; it shows up in every node in this family, so knowing it will save you from typing the correct spelling into ComfyUI's search bar and getting nothing.