Replace the hardcoded green-screen auto-detection with a general flat-colour
detector. When screen_color is null the background colour is now detected from the
image border (dominant colour of the border strip) and used directly as the chroma
model, with a failure gate that raises when the border is not one clean flat colour
(gradient / texture / subject filling the frame).
- chroma: add detect_background_color + _background_border_cluster; the null case of
estimate_background_model samples the detected cluster directly (no seed search);
compute_bg_confidence is now always perceptual (Lab/RGB distance). Removed the green
heuristic (initial_green_candidates), the green multiplicative gating, the now-unused
_smoothstep, and five green-only ChromaSettings fields.
- pipeline: reuse the detected colour for de-spill in the auto case.
- settings / default.yaml: add detect_* tuning fields; refresh screen_color docs.
- README: document auto-detection + the failure gate, trimap modes, birefnet config.
A supplied --screen-color hex still uses the seed-search refinement. Validated:
detects green / pastel / text samples correctly, raises on gradient / two-colour, CLI
exits 1 on failure, green and pastel mattes unchanged in quality.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
lhk229
62f175948e