Preview Image

If you've built one workflow, you've dropped in a Preview Image at the end of a branch without thinking. Preview Image shows your images in the ComfyUI interface without committing them to your output folder. It's the sibling of Save Image with the "actually keep this" part removed, and the distinction is the whole point - and the source of most of the confusion around it.

What it is

One input, images. It renders the tensor to a preview in the UI and also writes the file to disk - but to ComfyUI's temp directory, not your output folder. The mechanism, straight from the source: it subclasses Save Image, points its output at the temp directory, appends a random _temp_xxxxx prefix so it can't collide, and uses light compression. The node's own description puts it bluntly: "Preview the images without saving them to the ComfyUI output directory." The images output passes the tensor through untouched, so you can preview mid-graph and keep feeding the same images onward.

The temp files are exactly that: temporary. They're cleared on restart. If you've ever gone hunting for a previewed image and couldn't find it in output/, it was in ComfyUI/temp/ and got wiped - this is the single most common "where did my image go" moment in ComfyUI, and it's not a bug.

Preview vs. Save, made practical

The mental model that keeps you out of trouble: Preview Image is for looking, Save Image is for keeping. People who generate a lot and cull aggressively live on Preview Image - no disk clutter from the 40 drafts you'd never keep, just one folder of the 3 you did. People who need every output (training data, batch work, client deliverables) use Save Image. The standard setup is both on the same branch: Preview at the end so you can look, Save Image alongside with a %date% prefix so the keepers actually land in output/.

The temp-directory fact also enables a workflow worth knowing: you can preview first, decide after the fact which ones to keep, and grab them from ComfyUI/temp/ before restarting. The community has been doing exactly this - "all your generated images are saved in the ComfyUI/temp folder, it's just cleared when you restart" - as a poor man's selective-save. Restart clears it, so move what you want before you do.

Getting it and the gotchas

Ships with ComfyUI core, a founding-era node in nodes.py - no install, no model files. Gotchas in order of frequency:

1. Thinking preview = saved. It's not in output/; it's temp, and it's gone on restart.
2. The metadata isn't embedded the way Save Image embeds it. Save Image writes your full workflow JSON into the PNG - that's the "drag an image back in and the graph reconstructs" trick that defines workflow sharing. Preview's temp files are for looking, not for sharing, so don't treat a preview as a shareable artifact.
3. One input, no extras. No filename prefix, no format choice, nothing to configure - if you find yourself needing those, you want Save Image (Advanced).

There's genuinely nothing to configure here, which is the point: it's the lowest-friction way to see what your graph made.