🔧 Mask Blur

Hard-edged masks are the number-one cause of visible seams in inpainting and compositing. Mask Blur softens (feathers) a mask's edges so the transition between the changed and unchanged regions blends instead of announcing itself with a sharp line. It's a tiny node you'll end up using in nearly every mask-based workflow.

Why you'd reach for it

When you inpaint or composite, the mask decides where the new content meets the old. A crisp binary mask makes that boundary abrupt - you get a halo, a color step, an obvious cut. Feathering the mask fades the boundary over a few pixels so the blend reads as natural. This is bread-and-butter for clean inpainting: mask the region, blur the mask, then inpaint or paste. Anyone who's fixed a face or swapped a background and seen an ugly outline around it wanted this node in the chain.

How it works

It applies a Gaussian blur to the mask. amount is the blur radius in pixels - how wide the feathered transition is. Small values (a few pixels) give a tight, subtle feather; larger values spread the boundary out for a very gradual blend. Because a blurred mask has partial (gray) values at its edges instead of pure black/white, downstream nodes treat those edges as partial strength, which is precisely what produces the smooth handoff.

Inputs and outputs

Input is mask, output is MASK - it slots straight into a mask pipeline. Two settings: amount (the feather radius, default 6, which is a reasonable start for portrait-scale work) and device, which lets you choose where the blur runs - auto, cpu, or gpu. For big masks or big batches, forcing gpu can speed things up; auto is fine for everyday use.

Installing it

Ships in ComfyUI Essentials by cubiq (Matteo Spinelli, the IPAdapter node author). ComfyUI Manager: search ComfyUI Essentials, install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/cubiq/ComfyUI_essentials

then restart. It appears as 🔧 Mask Blur under essentials/mask, class MaskBlur+. The pack has been maintenance-only since April 2025 - no worries for a node this stable.

Common issues

Getting the amount right is the whole game. Too little and the seam is still visible; too much and your mask bleeds into areas you meant to keep, softening detail beyond the region you wanted to touch. Scale the blur to your image size - 6px on a 512 image is very different from 6px on a 2048 upscale. If your feather looks fine on preview but the composite still shows an edge, the mask may not be the culprit: check that the node consuming the mask actually honors partial values (some paste nodes threshold the mask back to binary). And if you want the softened mask reflected in your graph before running the real op, pair this with Preview Mask to see exactly what you're feeding downstream.