Frequency Separation Hard Light LAB

Frequency separation is a retoucher's classic, and this node brings it into ComfyUI. Frequency Separation Hard Light LAB splits an image into two layers - a low-frequency layer (broad tone and color) and a high-frequency layer (fine texture and edges) - so you can edit each independently, then recombine them losslessly using a hard-light blend in LAB space.

Why you'd want it: it's the cleanest way to fix one thing without wrecking another. Smooth blotchy color or uneven lighting on the low-frequency layer and the pores, hair, and edges on the high-frequency layer stay razor sharp. Or sharpen texture without amplifying color noise. In RES4LYF's world it's a detail-transfer and cleanup tool - part of the same family as Image Channels LAB and Image Median Blur - and it's how you carry crisp detail from one image onto the tone of another.

How it works

Classic frequency separation: the low-pass layer is a blurred version of the image (broad tone), and the high-pass layer is what's left over (the fine detail), stored so that hard-light-blending it back over the low-pass reconstructs the original exactly. This node handles both the split and the recombine, working in LAB so luminance detail stays separate from color. Feed it an original to split; feed it edited low- and high-pass layers to rebuild.

The inputs and outputs that matter

All inputs are optional because the node runs in two directions:

• original (IMAGE, in) - provide this to separate; read the high_pass and low_pass outputs.
• low_pass / high_pass (IMAGE, in) - provide these (typically after editing one) to recombine; read the original output as your finished image.
• Outputs: high_pass, original, low_pass (all IMAGE).

The workflow is a loop: split → edit the low-pass (blur, color-correct, replace) and/or the high-pass (sharpen, transfer) → feed them back to get a clean original out.

How to install it

ComfyUI Manager: search RES4LYF, install, restart. Manually:

cd ComfyUI/custom_nodes
git clone https://github.com/ClownsharkBatwing/RES4LYF
cd RES4LYF
pip install -r requirements.txt

Portable ComfyUI: use the embedded pip. Restart, hard-refresh F5. No downloads.

Common issues & troubleshooting

Recombine doesn't match the original. Frequency separation is only lossless if the high-pass is reunited with the same low-pass it was derived from (or a deliberately edited one). Mixing a high-pass from image A with an unrelated low-pass will look off - that "off" is actually the feature when you're doing detail transfer, but it surprises people expecting a clean rebuild.

Halos or edge artifacts. These come from the blur radius used to make the low-pass, not from the recombine. If you're generating the low-pass with Image Median Blur, a too-large size can introduce edge halos. Tune the blur.

The high-pass looks like flat gray. Correct - a high-pass layer is mostly mid-gray with detail riding on top. You don't view it directly; you blend it back. Judge the result after recombining.

Where to start. Split the original, blur or color-correct the low-pass, leave the high-pass untouched, recombine. That single move - cleaning tone while preserving every bit of texture - is what frequency separation is for, and it's the reason this node exists in a detail-focused pack.