ACES IO — Preview

ACES IO - Preview is the humblest node in this pack, and it does one useful thing: shows you an image inline while passing it through unchanged. It's functionally ComfyUI's built-in PreviewImage, but living in the ACES IO menu so it sits naturally at inspection points in your color-management chain.

The whole interface is one input, image, and one output, image. You drop it anywhere - between the ColorSpace node and your sampler to eyeball the ACEScg intermediate, or after the Viewer to check the display result - and the tensor flows through unmodified, so it never interrupts the graph. Because it's an output node, the image thumbnail renders in the UI, and thanks to the pack's no-caching behavior it refreshes on every run, which is exactly what you want from a debug view.

Why not just use PreviewImage?

Fair question. If you already have the built-in preview, this node's only real advantages are convenience and discoverability: it's in the same ACES IO menu as the rest of the pack, and if you're building ACES workflows on a shared template, one menu means fewer "which menu is that under again" moments. It's also a handy final image output when you want a workflow that ends in a visible result without adding the core preview node to your imports. That's it - it's a convenience node, not a secret weapon, and there's no shame in skipping it.

The one thing worth remembering: it previews, it doesn't transform. Previewing a scene-linear ACEScg image here will look dark and desaturated because you're staring at raw linear values. If that's what's confusing you, the Viewer node (with its display transform + exposure/gamma) is the "look at it correctly" tool; Preview is the "just show me this exact tensor" tool. People mix the two up constantly, and it's the source of half the "why does my EXR look grey" posts.

Install

In BISAM20/ComfyUI-ACES-IO, same as every node in the pack: ComfyUI Manager → Install Custom Nodes → search ComfyUI-ACES-IO, restart. Manual: git clone https://github.com/BISAM20/ComfyUI-ACES-IO into ComfyUI/custom_nodes, then pip install -r requirements.txt. The only install gotcha that matters here is PyOpenColorIO (pip package opencolorio - Manager's hook installs it for you; without it the whole pack's nodes fail to register). No models, no downloads.