Preview Core

Stock ComfyUI previews are one-size-fits-all: a fixed box, no zoom, no background control, and if your image is a tall portrait it gets squished into a square like it owes somebody money. SickOllie's Preview Core is the Studio-family answer - a preview node with actual display options that still passes your image through untouched, so you can drop it anywhere in the graph without changing the pixels.

What it actually does

SOFitPreviewStudio is a dressed-up version of ComfyUI's stock PreviewImage. It's registered only in the Studio workflow, and it's the reason old Classic SOFitPreview nodes auto-upgrade to this one when you load a legacy workflow - the pack converts them in place, wiring and stored previews intact. It's an output node (it's the end of a branch), but the important detail is that it returns images unchanged: the preview you're looking at and the image flowing to your Output Core are the same tensor.

Under the hood it still calls ComfyUI's standard save-and-preview path with a SickOllieFitPreview prefix, so it shows up in your output folder like any preview would. What the widgets add is how the frontend draws it.

The inputs that matter

• images (required) - the IMAGE you want to look at.
• fit_mode - the headline control, six ways to frame the image: Contain + Upscale (default), Cover, Fit Width, Fit Height, Stretch, and Actual Size. Contain is what most people want: the whole image visible, scaled up to fit. Stretch is the one that will silently mangle aspect ratios if you aren't paying attention.
• background_mode - Solid, Checkerboard, or Blurred Image. The checkerboard is the honest way to eyeball whether the model baked in artifacts near transparent edges; Blurred Image fills the letterbox area with a blurred version of the image itself, which looks great in demos.
• background_color - hex color for Solid mode. Default #111111.

The single images output passes through to whatever you'd wire next.

Installing it

It's part of the SickOllie pack, so install the pack once:

cd ComfyUI/custom_nodes
git clone https://github.com/sickollie/SickOllie

or grab it via ComfyUI Manager (search "SickOllie"). Restart ComfyUI and Ctrl+F5 hard-refresh the browser tab. Python 3.10+ and a current LiteGraph canvas are the requirements; no extra pip installs for this pack.

The part the tooltip won't tell you

The node itself is simple, but in the Studio workflow it's a dock, not a docked node. The preview pane picks up persistent previews that survive reopening the workflow, plus pin, side-by-side compare, a "Library Thumb" action that assigns the displayed image to the active main LoRA, and a "Recipe" quick-save that stores the displayed image's resolved Studio setup. Those live in the JS dashboard, which is also why the README is so insistent about the hard refresh: an old cached frontend shows you a bare viewer with none of the toolbar.

Where people get tripped up: expecting the preview to alter the image, or treating it as a save node. It does neither. It's the one node in the Studio chain you can reroute, bypass, or delete and the rest of the graph shrugs. Use it for exactly what it's for - actually seeing what you made.