Pull alpha toward 0 in the unknown band where bg_confidence is high, so green
that survives in hair gaps and hole pockets goes transparent (doc section 10).
Runs between trimap enforcement and alpha cleanup; sure-foreground pixels are
never touched, keyed by the bg_confidence we already compute.
On the two samples this clears the faint outer green halo (edge pixels
19.3k -> 16.0k) but has little *visible* effect, because their residual is no
longer green: it is magenta from the pymatting unmix on genuine semi-transparent
hair (vis-magenta p95 ~0.07, identical pre/post despill), which this pass
deliberately leaves alone. The magenta needs a separate colour fix.
Knobs live in AlphaPostSettings (chroma_suppress*, default on).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
After the full-foreground despill (5ddf0cd) the residual green was confined to
semi-transparent hair (alpha < 0.5): 85% of the worst pixels had alpha < 0.3,
where a pixel-wise unmix (divide by small alpha) is too noisy to trust.
Replace the hand-rolled unmix/local-blur estimator with pymatting's
estimate_foreground_ml (Germer et al. multi-level closed form), which propagates
reliable foreground colour from high-alpha neighbours into the fringe and
estimates the background, so green spill is unmixed rather than clamped. The
despill pass stays as a light cleanup on top.
- foreground.method selects "ml" (default) or "unmix" (legacy heuristic kept as
a fallback when pymatting is unavailable, matching the chroma fallback idiom).
- ForegroundEstimate now exposes rgb (F), background (B) and a correction map;
debug outputs become foreground_rgb / foreground_background / foreground_correction.
Controlled comparison (same ViTMatte alpha, only foreground method changed),
edge_green_excess:
TestImage p95 0.176->0.031, mean 0.061->0.005
TestImage2 p95 0.165->0.004, mean 0.052->0.002
Adds pymatting (pulls in numba) to requirements.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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
Codex