👁️ Preview Image + (nhk)

Preview Image + (nhk) does a deceptively simple thing the core node won't: it shows you an image and hands the same image to the next node. The built-in PreviewImage is a terminal - it renders the image, then stops. This one renders and keeps the data flowing, which is exactly what you need when you want to eyeball a result mid-pipeline without ending the branch.

This is part of the pack's experimental image-evaluation workflow (the author's own docs mark these as WIP and warn the behavior may change). In that setup it's used to preview the image being evaluated while the evaluation result still flows onward for conditional routing.

How it works

Mechanically it's the simplest thing in the pack: one images input, one image output, and a preview render in between. Nothing gets processed, downsampled, or resampled - the exact tensor that goes in comes out. It's a pass-through with a viewport attached, and is_output_node is false, which matters more than it sounds: it is not itself a terminal.

That last point is the pack's own documented trap. From IMAGE_EVALUATION.md: ComfyUI executes backward from terminals - only chains that lead into a node marked OUTPUT_NODE=True actually get pulled into the graph. Preview Image + is not such a node. If you connect it and nothing downstream runs, you almost certainly don't have a real terminal (a standard Save Image or PreviewImage) reachable from the branch. The passthrough preview alone won't hold the graph open.

Inputs and output

• images - the IMAGE tensor you want to look at.
• image - the same tensor, passed through unchanged, ready to feed a router, evaluator, or the next processing step.

That's the whole interface. No sliders, no formats, nothing to configure.

Installing it

Like every node in this pack:

cd ComfyUI/custom_nodes && git clone https://github.com/Enashka/ComfyUI-nhknodes

restart, or install "NHK Nodes" from ComfyUI Manager. No extra dependencies. It'll appear under nhk/wip, not with the stable nodes - the author flags the whole evaluation family as experimental while they sort out the pull-based execution quirks.

The gotcha worth remembering

If you're used to core PreviewImage being a safe place to end a branch, unlearn that here. This node is explicitly not a terminal, and the failure mode is silent: the preview may not even fire if nothing downstream pulls the branch. When you're building an evaluation flow, keep one real terminal on the line. And treat the nhk/wip label seriously - these nodes are version 0.x territory and the author says behavior may change while the reverse-dependency execution model gets worked out.