The band (dilate-minus-erode ring on the seg silhouette, added in 5f48f7a)
was meant to give ViTMatte room to anti-alias the boundary. Measured on a
warm-background sample (fix_image02, #FFD6C2): ViTMatte outputs near-binary
alpha in the band on crisp-edged anime images (96% hard values, 82% of
silhouette crossings with zero soft pixels), so the band delivered no
anti-aliasing -- it only let ViTMatte relocate the boundary (chewed edges)
and wholly confiscated structures thinner than the ring: 74% of lost hair
strand pixels were rule-FG demoted by the overwrite, then dropped by
ViTMatte. Without the band, 88% of those strands survive, edges follow the
rule-decided contour, and cross-check no longer bites strand edges because
strand cores stay anchored at 255 (re-destroyed: 0 px).
The rules own unknown pixels (background-hued blends, low-seg transitions)
remain ViTMatte territory. fuse_trimap (seg mode) keeps its band untouched --
its rules were designed around it and the removal is only validated for the
directional path.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
lhk229
f1a083349b