Why does my SpriteMask leave a halo at the edge?

Alpha Cutoff is binary — pixels above pass, below cut. Antialiased edges have intermediate alpha that gets rounded to one or the other, producing a fringe. Tune Alpha Cutoff or pad your mask sprite with a fully transparent border.

What Alpha Cutoff value works?

0.1 lets most edge pixels through; 0.5 cuts more aggressively. Match to your sprite's alpha distribution. For pixel art, 0.5 is fine; for soft sprites, 0.1 preserves the silhouette.

Should I use premultiplied alpha?

For straight-alpha sprites (most PNG), no. For premultiplied sources, yes. SpriteMask Alpha Cutoff samples the source's alpha channel directly; mismatch produces fringe.

Fix: Unity SpriteMask Alpha Cutoff Edge Fringe

Quick answer: Lower Alpha Cutoff to 0.1 (or 0.01 for very soft masks). Pad mask sprite with a transparent border so edges have room to fade. Avoid premultiplied alpha unless source matches.

SpriteMask cuts cleanly inside but leaves a halo at the edge. Antialiased pixels round to one side of Alpha Cutoff and produce a fringe.

The Symptom

Visible 1–2 pixel band of wrong color around the masked region. Worsens with sharper masks; smoother with lower Cutoff.

The Fix

SpriteMask Inspector:
  Alpha Cutoff:    0.1      // preserve soft edges
  Front Sorting Layer / Order: as needed

0.1 keeps most edge pixels visible. Resulting mask blends naturally instead of cutting.

Sprite Border Padding

If editing the source mask art, add 4–8 px transparent border around the visible content. Atlas packing won’t bleed neighbor sprites; mask edges stay clean.

Verifying

Place mask over a high-contrast background. Edge should fade smoothly, not show a halo. Tweak Cutoff until match.

“Cutoff low. Border padded. No fringe.”

Related Issues

For SpriteMask not clipping, see not clipping. For 2D Light shadow caster, see shadow caster.

Cutoff right. Edge clean.