Nuke Viewer

In Nuke, the Viewer is where you live - the window that shows you the image and lets you flip between channels to check your matte. ComfyUI doesn't have a built-in equivalent that behaves that way, so this pack ships NukeViewer: a node that takes an image and outputs a version of it showing just the channel you care about, with gamma and gain applied. You drop it on the canvas, wire its output to a preview, and suddenly you can actually see your alpha or your red channel as a real image.

One thing to get straight up front: it doesn't open a separate window or act as a "viewer" in the interface sense. It outputs an IMAGE - a transformed copy of your input. That's why it's still useful: you can put it inline in a workflow and have a preview node show you exactly what a channel looks like at that point in the graph.

When you'd reach for it

• Checking your alpha - the classic move. Wire a mask or a cutout through with channel set to alpha, and you see the matte as black-and-white. Holes, hard edges, and garbage become obvious instantly.
• Inspecting a single color channel - is that red fringe real or am I imagining it? Set channel to red and you'll know.
• Previewing with gamma/gain - brighten a dark render just for viewing without altering the actual data flowing downstream. That's what a viewer is for: look without touching.

The inputs that matter

• channel - rgba, rgb, red, green, blue, alpha, or luminance. The one you'll actually use.
• gamma - 0.1 to 3, applies a display gamma so you can see into dark regions.
• gain - 0.1 to 5, multiplies brightness for viewing.
• show_overlay / overlay_text - optionally stamp a text label onto the output, handy when you're comparing several views side by side and can't remember which is which.
• mask - optional IMAGE mask to restrict where the viewing transform applies.

Output is a single IMAGE (the processed view), ready for a preview or save node.

Installing it

It's part of the Nuke Nodes pack:

cd ComfyUI/custom_nodes
git clone https://github.com/sumitchatterjee13/nuke-nodes-comfyui.git nuke-nodes
cd nuke-nodes
pip install -r requirements.txt

Or search "Nuke Nodes" in ComfyUI Manager and restart. It's under the Nuke category, a pure PyTorch node with no special dependencies.

Common issues

• "It doesn't open a viewer window" - right, it's not that kind of viewer. Wire the IMAGE output into a preview node. The point is the channel inspection, not a separate UI.
• The alpha looks flat or wrong - alpha is a single channel rendered as grayscale; if your image has no real alpha (most RGB-only generations), it'll just be white. That's informative in itself.
• Gamma does nothing visible - it only affects the viewing transform on the output; if you wanted to permanently brighten the image, this isn't the node (NukeExposure is).

For anyone who's ever had to "trust" that a mask was clean without seeing it, this node turns guessing into looking.