Preview Image (Alpha)

ComfyUI's stock Preview Image node doesn't render an alpha channel - it just shows you RGB, so anything that's genuinely meant to be transparent (a cutout character, a rendered sprite, a matte you're building for compositing) either looks solid and opaque in preview or gets its transparency silently dropped from what you're looking at. That's a real problem when you're building alpha by hand: you can't tell if your matte is any good until it's already been exported somewhere else. Preview Image (Alpha) fixes exactly that - it composites the alpha in so you can actually judge the cutout before it goes anywhere.

What it's for

Anywhere in this pack's video/masking workflow where you're producing or manipulating transparency - after Replace Alpha injects or swaps a mask into your frames, before frames head off to Spritesheet Builder or a save node - this is the checkpoint. Catching a bad matte here, where you can see it, is a lot cheaper than catching it after it's baked into an exported spritesheet or archive.

The inputs and outputs that matter

Two required inputs, no widgets to configure:

• frames (IMAGE) - the image or batch you want to preview.
• alpha (MASK) - the transparency to composite in alongside it.

There are no outputs - is_output_node is true, same as the stock Preview Image node. It's a terminal display step, not something you chain further work off of.

How to install it

Search "Link Comfy Nodes" in ComfyUI Manager and install from there. Or by hand:

cd ComfyUI/custom_nodes
git clone https://github.com/Mister-Link/link-comfy-nodes
pip install -r link-comfy-nodes/requirements.txt

Restart ComfyUI. No extra models or heavy dependencies for this node specifically.

Common issues & troubleshooting

Frames and alpha need to line up. Both inputs need matching batch size and dimensions - a mismatch between how many frames you're previewing and how many masks you're feeding it is the most likely source of an error here, the same as with any node in this pack that takes separate image and mask streams.

You have RGBA baked into one image, not a separate mask. This node takes alpha as a MASK type specifically, not a 4-channel image with transparency built in. If your source is a loaded RGBA PNG rather than a plain image plus a separate mask, split the alpha channel out first with a standard ComfyUI convert/split node before wiring it in here.

Confusing this with a real alpha-fix node. Preview Image (Alpha) only shows you what you already have - it doesn't repair, generate, or clean up a mask. If your alpha is wrong, fix it upstream (Replace Alpha, a segmentation node, hand-painted mask) and come back here to confirm the fix worked, rather than expecting this node to do anything but display.