Green spill bleeds into pixels ViTMatte marks as solid foreground (alpha~1),
but despill was gated to the soft edge band (0.005<alpha<0.995) and weakened
exactly there: the alpha tent peaked at 0.5 and bg_confidence (low on the
character edge) further suppressed the correction.
- (1) Apply despill to the whole foreground (alpha > edge_low) instead of the
soft band only; neutral pixels stay untouched via the green-excess term.
- (2) Weight by alpha at full strength across the opaque range (alpha>=0.5),
easing off only where mostly transparent, instead of a tent peaking at 0.5.
- (3) Drop bg_confidence as a despill gate; localise purely by green excess.
Controlled comparison (same alpha, only despill changed), edge_green_excess:
ViTMatte TestImage p95 0.239->0.176, mean 0.131->0.061
ViTMatte TestImage2 p95 0.231->0.165, mean 0.115->0.052
Removes now-unused DespillSettings fields edge_high and bg_confidence_weight.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
lhk229
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