Widen the boundary gate and tighten thresholds — the rim ran 2px deep

spritekit.py

@@ -185,8 +185,8 @@ def suppress_residual(
     rgb: np.ndarray,
     alpha: np.ndarray,
     key_rgb: np.ndarray,
-    low: float = 0.45,
-    high: float = 0.80,
+    low: float = 0.25,
+    high: float = 0.45,
 ) -> np.ndarray:
     """Drive alpha to zero wherever the *final* color is still the backdrop.
 
@@ -214,8 +214,10 @@ def suppress_residual(
         return alpha
     direction = key_chroma / magnitude
     fraction = np.einsum("...c,c->...", to_ycc(rgb)[..., 1:], direction) / magnitude
-    # High where transparency is nearby, ~0 anywhere inside the character.
-    boundary = _smoothstep(0.15, 0.55, 1.0 - _box_blur(alpha[..., None], 3)[..., 0])
+    # High where transparency is nearby, ~0 anywhere inside the character. The radius has to reach several pixels
+    # inward: measured across a real edge, the rim ran two pixels deep at alpha 0.85 and 0.99, and a tighter gate
+    # had already decayed to 0.16 by the second one and left it standing.
+    boundary = _smoothstep(0.05, 0.35, 1.0 - _box_blur(alpha[..., None], 6)[..., 0])
     return (alpha * (1.0 - boundary * _smoothstep(low, high, fraction))).astype(np.float32)