Ephemeral Preview (Low RAM)

ComfyUI's normal preview nodes write a new PNG to temp every time they run. Run a long batch or a live animation loop and you end up with thousands of PreviewImage_00001_.png files eating your disk. This node is the low-RAM answer: it previews the image, then overwrites the same fixed file every run instead of accumulating new ones. One image slot, always fresh. That's the entire pitch, and it's a good one for anyone who leaves ComfyUI cranking overnight.

How it works

The implementation is small and deliberate. For each image in the batch it converts the tensor back to a PIL image, saves it to ComfyUI's temp directory under a fixed name - ephemeral_monitor_0.png, ephemeral_monitor_1.png, and so on - with optimize=True and a moderate compression level, then returns a ui dict shaped exactly like ComfyUI's built-in PreviewImage node so the frontend displays it normally.

The fixed filename is the point: disk usage stays constant regardless of how many times the node runs. There's a slightly clever detail in how it forces the browser to refresh while keeping the file name stable - the display is keyed to refresh on each run even though the file on disk doesn't change. So you get a live-updating preview with a constant footprint. The author named it "Ephemeral Preview (Low RAM)" and the low-RAM claim is accurate in the sense that matters: no runaway temp accumulation.

Inputs and outputs

One input: images (IMAGE). That's it. It's an output node, so there are no outputs to wire - it's a terminal node, the ComfyUI way of saying "display this." Hang it off any IMAGE output in your graph where you want to watch progress without building up a file pile.

Install

Part of the ComfyUI_EmAySee_CustomNodes pack. ComfyUI Manager → search "EmAySee" → install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/EmAySee/ComfyUI_EmAySee_CustomNodes

No requirements, no models - it uses only PIL/numpy, which ComfyUI already bundles. Restart and you'll see the pack's "SPECTRE v5.0" banner in the console.

The honest take

The trade-off is exactly what you'd expect: because the file is overwritten, you don't get ComfyUI's normal history of previews. If you want to scrub back through what the model produced at step 5 vs step 50, this is the wrong tool - use a normal preview or the built-in image history. If you want to watch a long run without your temp folder turning into a landfill, this is the right one. It's a niche, but it's a niche that exists. One caveat: it only holds one image per index, so multi-image batches show the last state of each slot, not a history.