Sharpen (mtb)

Diffusion output can come out a touch soft - especially after a VAE decode, an upscale, or a blur-heavy step. Sharpen (mtb) is the node that puts the crispness back. It's a straightforward unsharp-mask sharpener with enough knobs to control how aggressive it gets, so you can add a subtle bit of bite or really crunch the edges.

Where it fits: as a finishing touch near the end of a graph, or right after an upscale that left things a little muddy. It's the kind of node you don't think about until an image looks "almost there but a bit soft," and then it's exactly what you want. Keep it gentle for photoreal work; a heavy hand makes halos and looks obviously processed.

It's in the image-processing section of MTB Nodes (comfy_mtb) by melMass, next to Blur and Color Correct.

How it works

Unsharp masking works by blurring a copy of the image, subtracting that blur to find the edges, and adding the edges back with extra contrast - which is why a sharpen node has blur parameters. This one builds a Gaussian kernel from a radius and sigmas, and alpha controls how strongly the recovered edge detail is added back. Bigger kernel and sigma = the sharpening acts on broader features; higher alpha = more punch. It's a tensor operation, no model involved.

The inputs and outputs that matter

• image - what you're sharpening.
• alpha (default 1) - strength. This is the main dial. Below 1 for a subtle lift, above 1 for aggressive sharpening. Push it too far and you get white halos around edges - back off when you see them.
• sharpen_radius (default 1) - the size of the sharpening kernel. Small values sharpen fine detail; larger values sharpen broader structures (and start looking crunchy).
• sigma_x / sigma_y (both default 1) - the spread of the Gaussian in each direction. Equal values sharpen evenly; you can bias one axis, but for normal work leave them matched.

Output is a single IMAGE. Drop it near the end of your chain, just before saving.

How to install it

ComfyUI Manager: search MTB Nodes, install, restart. Manual:

cd ComfyUI/custom_nodes
git clone https://github.com/melMass/comfy_mtb

then restart. Pure Torch/Python - no models, nothing extra to install.

Common issues & troubleshooting

Ugly halos around edges. The classic over-sharpening artifact: bright fringes hugging high-contrast edges. Lower alpha, and shrink sharpen_radius. Sharpening is one of those effects where less is almost always more for a natural look.

Noise got sharper too. Sharpening amplifies whatever's there, including grain and compression noise. If your source is noisy, denoise (or sharpen more gently) - otherwise you're just making the noise crisp.

No visible change at defaults. alpha 1 with radius 1 is a mild effect. If you can't see it, nudge alpha up gradually rather than jumping to a big number that overshoots into halos.

Sharpen-then-scale undoes it. If you sharpen and then downscale afterward, the resize softens what you just added. Do the sharpen last, at final resolution, so it survives to the output.