Mask Morphology

Grow a mask, shrink it, fill small gaps, remove thin spurs, or extract just its outline. It is the mask version of Photoshop's Select → Modify → Expand / Contract.

In ComfyUI	Add Node → ComfyUI-JH-PixelPro → mask → Mask: Morphology
Good for	Expanding a mask to cover halos, contracting to remove a fringe, closing small holes, making an edge band

When to use it

Morphology changes the shape of a mask rather than its softness. The idea is to slide a small round "brush" (the kernel) across the mask edge. Seven operations are available:

Operation	What happens	Typical use
dilate	Mask grows outward	Cover a halo; make room for a feather
erode	Mask shrinks inward	Remove a coloured fringe at the edge
open	Erode, then dilate	Delete small white specks and thin spurs
close	Dilate, then erode	Fill small black holes and gaps
gradient	Dilated minus eroded	An outline band around the edge
tophat	Original minus open	Keeps only the small bright bits that open would remove
blackhat	close minus original	Keeps only the small dark gaps that close would fill

For removing specks or holes by their size (rather than by brush radius), Mask Cleanup is easier to control.

Quick start

1. Connect any mask to Mask Morphology.
2. Pick erode with radius 3 to shrink the selection and trim an edge fringe, or dilate to expand it.
3. Preview with Mask Preview.

Settings

Setting	Default	What it does	Tip
operation	dilate	Which of the seven operations to run.	See the table above.
radius	3	Radius of the round kernel, in pixels.	1 to 64. Roughly how many pixels the edge moves.
iterations	1	How many times to repeat the operation.	1 to 10. For big changes, a larger radius is usually cleaner than many iterations.

Output: mask (MASK).

Tips from retouching

• To make a feathered ring around the edge, run gradient, then soften it with Mask Edge Smoother or Sub-Pixel Mask Refiner.
• After dilate or erode, the edge can look jagged. Finish with a feather.
• Use close before building a Trimap if your mask has pin-holes.
• Morphology also works on soft masks: it grows and shrinks the grey values (a grayscale dilate takes the local maximum).

Under the hood

An elliptical structuring element of size 2 * radius + 1 is built with cv2.getStructuringElement. dilate and erode call cv2.dilate and cv2.erode; the other operations use cv2.morphologyEx. It runs on the CPU in float32, one batch item at a time, and the result goes back to the input device. Source: core/mask_morphology.py. For very large radii on the GPU, avoid kornia.morphology; it uses a lot of memory.

Related nodes

• Mask Cleanup for removing specks and holes by size
• Mask Combine to merge the result with another mask
• Trimap Builder for three-zone maps
• Mask Edge Smoother to smooth the result

Example workflow

Mask Morphology example workflow. Copy workflows/sample_portrait.jpg and workflows/sample_binary_mask.png into ComfyUI/input/. It runs close at radius 64 to seal the small shadow gap by the nose without growing the outline. It uses only core ComfyUI nodes and this pack.