⚗ Alchemica · Number previews

This is the smallest node in the pack and it solves a problem you've had and dismissed. AlchemicaKrea Pro can generate a batch of composition previews on consecutive seeds - 8 low-res candidates in one queue. They come back as a batch in one image grid, and your job is to pick the good one and type its number into the scelta field. So you're squinting at eight near-identical framings trying to work out which tile is index 5, and the batch tile order is not something you want to be reasoning about.

Plug this node in and every tile says #k seed <number> in the top-left corner. Read the number, type it into scelta, done.

The inputs

images - any IMAGE, typically the batch that came out of a preview run (or anything else you want labelled).

seed_base - the seed the batch started from. It's marked forceInput, meaning it's meant to be a wire rather than a number you type: connect it to the seed output family your preview run used - the seed widget on AlchemicaKrea Pro converted to an input, or the seed_usato output of a previous run - and each tile is labelled with seed_base + k, which is exactly the arithmetic the previews themselves use.

That last point is the bit worth catching. The previews are seeded seed, seed+1, seed+2…, so the number burned into tile k is the seed that would reproduce that tile, not merely the tile's index. If you'd rather keep the exact seed of a preview you liked instead of using the two-pass scelta ritual, this output is where you read it off.

The output

IMAGE - the same batch with the labels drawn on. It's a pure pass-through otherwise: the tensor shape and the batch order are unchanged, so it sits anywhere in an image chain. Font size scales with image height, so it stays legible on a 512-pixel preview and doesn't become absurd on a 4 MP final. The label drawn is a semi-transparent black box with white text, so it doesn't obliterate whatever is underneath.

Wiring

AlchemicaKrea Pro · latent → VAEDecode → ⚗ Number previews · images → Preview Image / SaveImage
AlchemicaKrea Pro · seed  ─────────────→ ⚗ Number previews · seed_base

Put it after the decode and before whatever you're looking at. If you're saving previews, note that the numbers are now in the pixels - which is the point, but don't run the final render through this node unless you want the label in the delivered image.

Installing

Part of the pack:

cd ComfyUI/custom_nodes
git clone https://github.com/Nessuno76/ComfyUI-AlchemicaSampler

Restart the ComfyUI server - the pack's nodes don't appear on a browser reload. It draws with PIL, which ComfyUI already ships, and the pack declares no Python dependencies of its own. ComfyUI 0.36.0 or newer for the pack as a whole.

Traps

Typing the seed instead of the tile number. scelta wants the index (0-255) that the previews used, not the seed value. If tile 5 shows seed 1053, you set scelta to 5 with the base seed unchanged - or you set the seed to 1053 and skip the preview machinery entirely. Both work; mixing them doesn't.

Forgetting it's a batch node. If your images come through one at a time, you get one label reading #0. That's not broken, it's just a batch of one.

Using it as a seed-saver for a full render. The preview seeds reproduce the preview's stage 1 exactly, but a preview is a low-resolution stage 2 with the same noise field. The scelta path regenerates properly at full size; re-running a preview's seed manually does not necessarily give you the same final image.