Presave Image

Every ComfyUI user hits the SaveImage-versus-PreviewImage fork in the road eventually. SaveImage commits a permanent PNG to output/; PreviewImage writes a throwaway to temp/ so you can iterate without burying your output folder in rejects. MKRPreSave is the pack's answer to that false choice: it's one node that starts life as a preview and flips into a real save when you're ready. Hence the name - it's a pre-save.

What it's for

You reach for it at the end of a chain when you're generating batches and want to (a) see what you made without polluting output/, and (b) still have a one-click path to real files with the quality settings you care about. The preview_only boolean defaults to true, which means out of the box it behaves like a PreviewImage. Uncheck it and it writes PNG/JPEG/WebP/GIF to output/<subfolder> instead. Same node, two lives.

It's also an output node that always runs - the source returns float("nan") from IS_CHANGED, which in ComfyUI terms means "rerun me every queue event, don't cache me away" (see the node-plumbing docs for why that trick works). And it ships a custom frontend via the pack's WEB_DIRECTORY, so the widgets you see are the author's own.

Inputs that matter

• preview_only - the whole gimmick. True = preview in temp, False = commit to disk.
• output_format - png, jpeg, webp, or gif. PNG is default, and the only one that embeds the workflow metadata (the "drag it back in and rebuild the graph" trick lives in the PNG text chunks).
• animation_mode - auto (decides from frame count and format), single_animation (one animated gif/webp from the batch), or per_frame (one file per frame).
• orientation + split_percent + fit_mode - this is the custom frontend's showpiece: a side-by-side split preview (horizontal or vertical, split at split_percent, contain/cover/stretch for fit). Great for before/after compares.
• save_mask - if you also feed the optional mask input, it can write the mask out too.
• filename_prefix, subfolder, overwrite - standard output plumbing. filename_labels (optional) lets you give frames their own names.

Compression/quality knobs: png_compress_level, jpeg_quality, webp_quality, and animation_fps + animation_loop for animated output.

Installing it

Pack-level install, unchanged:

cd ComfyUI/custom_nodes
git clone https://github.com/criskb/MKRShift_Nodes

then restart ComfyUI (or search MKRShift_Nodes in ComfyUI Manager). This node is pure PIL + torch - no ffmpeg needed, no extra requirements.

Common issues

The classic self-inflicted wound: you leave preview_only checked for a week, generate a whole batch, and nothing ever lands in output/. That's not a bug - flip the toggle. The reverse is also worth knowing: PNG embeds the workflow, but JPEG/WebP/GIF don't carry the graph, so if you care about "workflow included," keep your final deliverable PNG. And if you're animating, remember single_animation only produces an animated file for gif/webp - asking it for a single-animation PNG just gets you one still.