feat: coarse_stride per sub-sampling top-level

Nuovo kernel JIT _jit_score_bitmap_rescored_strided: valuta solo
pixel su griglia stride x stride al top della piramide. NMS + fase
full-res recuperano precisione. Speed-up ~stride^2 sulla fase coarse,
specie su scene grandi (1920x1080).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pm2d/_jit_kernels.py

@@ -111,59 +111,60 @@ if HAS_NUMBA:
         return acc
 
     @nb.njit(cache=True, parallel=True, fastmath=True, boundscheck=False)
-    def _jit_score_bitmap_greedy(
+    def _jit_score_bitmap_rescored_strided(
         spread: np.ndarray,
         dx: np.ndarray, dy: np.ndarray, bins: np.ndarray,
         bit_active: np.uint8,
-        min_score: nb.float32,
+        bg: np.ndarray,
-        greediness: nb.float32,
+        stride: nb.int32,
     ) -> np.ndarray:
-        """Score bitmap con early-exit greedy (no rescore background).
+        """Variante con sub-sampling: valuta solo pixel su griglia stride×stride.
+        Score restituito ha stessa shape (H, W); celle non valutate = 0.
 
-        Per ogni pixel iteriamo le N feature; abortiamo non appena diventa
+        4× speed-up con stride=2 (NMS recupera precisione in full-res).
-        impossibile raggiungere `min_required` count anche aggiungendo
+        Numba prange richiede step costante: itero su indici griglia e
-        tutte le feature rimanenti. min_required = greediness * min_score * N.
+        moltiplico per stride dentro il body.
-
-        greediness=0 → nessun early-exit (equivalente a kernel base).
-        greediness=1 → exit non appena hits + remaining < min_score * N.
-        Tipico: 0.7-0.9 → 2-4x speed-up senza perdere match.
         """
         H, W = spread.shape
         N = dx.shape[0]
         acc = np.zeros((H, W), dtype=np.float32)
-        if N == 0:
+        ny = (H + stride - 1) // stride
-            return acc
+        nx = (W + stride - 1) // stride
-        min_req = greediness * min_score * N
+        for yi in nb.prange(ny):
-        inv_N = nb.float32(1.0 / N)
+            y = yi * stride
-        for y in nb.prange(H):
+            for i in range(N):
-            for x in range(W):
+                b = bins[i]
-                hits = 0
+                mask = np.uint8(1) << b
-                for i in range(N):
+                if (bit_active & mask) == 0:
-                    b = bins[i]
+                    continue
-                    mask = np.uint8(1) << b
+                ddy = dy[i]
-                    if (bit_active & mask) == 0:
+                yy = y + ddy
-                        # Nessun chance per questa feature
+                if yy < 0 or yy >= H:
-                        if hits + (N - i - 1) < min_req:
+                    continue
-                            break
+                ddx = dx[i]
-                        continue
+                x_lo = 0 if ddx >= 0 else -ddx
-                    ddy = dy[i]
+                x_hi = W if ddx <= 0 else W - ddx
-                    yy = y + ddy
+                rem = x_lo % stride
-                    if yy < 0 or yy >= H:
+                if rem != 0:
-                        if hits + (N - i - 1) < min_req:
+                    x_lo += stride - rem
-                            break
+                x = x_lo
-                        continue
+                while x < x_hi:
-                    ddx = dx[i]
+                    if spread[yy, x + ddx] & mask:
-                    xx = x + ddx
+                        acc[y, x] += 1.0
-                    if xx < 0 or xx >= W:
+                    x += stride
-                        if hits + (N - i - 1) < min_req:
+        if N > 0:
-                            break
+            inv = 1.0 / N
-                        continue
+            for yi in nb.prange(ny):
-                    if spread[yy, xx] & mask:
+                y = yi * stride
-                        hits += 1
+                for xi in range(nx):
+                    x = xi * stride
+                    v = acc[y, x] * inv
+                    bgv = bg[y, x]
+                    if bgv < 1.0:
+                        r = (v - bgv) / (1.0 - bgv + 1e-6)
+                        acc[y, x] = r if r > 0.0 else 0.0
                     else:
-                        if hits + (N - i - 1) < min_req:
+                        acc[y, x] = 0.0
-                            break
-                acc[y, x] = nb.float32(hits) * inv_N
         return acc
 
     @nb.njit(cache=True, parallel=True, fastmath=True, boundscheck=False)
@@ -241,9 +242,8 @@ if HAS_NUMBA:
         _jit_score_bitmap(spread, dx, dy, b, np.uint8(0xFF))
         bg = np.zeros((32, 32), dtype=np.float32)
         _jit_score_bitmap_rescored(spread, dx, dy, b, np.uint8(0xFF), bg)
-        _jit_score_bitmap_greedy(
+        _jit_score_bitmap_rescored_strided(
-            spread, dx, dy, b, np.uint8(0xFF),
+            spread, dx, dy, b, np.uint8(0xFF), bg, np.int32(2),
-            np.float32(0.5), np.float32(0.8),
         )
         _jit_popcount_density(spread)
 
@@ -258,7 +258,7 @@ else:  # pragma: no cover
     def _jit_score_bitmap_rescored(spread, dx, dy, bins, bit_active, bg):
         raise RuntimeError("numba non disponibile")
 
-    def _jit_score_bitmap_greedy(spread, dx, dy, bins, bit_active, min_score, greediness):
+    def _jit_score_bitmap_rescored_strided(spread, dx, dy, bins, bit_active, bg, stride):
         raise RuntimeError("numba non disponibile")
 
     def _jit_popcount_density(spread):
@@ -291,46 +291,34 @@ def score_bitmap(
 
 def score_bitmap_rescored(
     spread: np.ndarray, dx: np.ndarray, dy: np.ndarray, bins: np.ndarray,
-    bit_active: int, bg: np.ndarray,
+    bit_active: int, bg: np.ndarray, stride: int = 1,
 ) -> np.ndarray:
-    """Score bitmap + rescore fusi in un solo pass (JIT)."""
+    """Score bitmap + rescore fusi in un solo pass (JIT).
+
+    stride > 1: valuta solo pixel su griglia stride×stride. Le celle non
+    valutate restano 0 nello score map. Pensato per coarse-pass al top
+    della piramide; il refinement full-res poi recupera precisione.
+    """
     if HAS_NUMBA and len(dx) > 0:
+        spread_c = np.ascontiguousarray(spread, dtype=np.uint8)
+        dx_c = np.ascontiguousarray(dx, dtype=np.int32)
+        dy_c = np.ascontiguousarray(dy, dtype=np.int32)
+        bins_c = np.ascontiguousarray(bins, dtype=np.int8)
+        bg_c = np.ascontiguousarray(bg, dtype=np.float32)
+        if stride > 1:
+            return _jit_score_bitmap_rescored_strided(
+                spread_c, dx_c, dy_c, bins_c, np.uint8(bit_active), bg_c,
+                np.int32(stride),
+            )
         return _jit_score_bitmap_rescored(
-            np.ascontiguousarray(spread, dtype=np.uint8),
+            spread_c, dx_c, dy_c, bins_c, np.uint8(bit_active), bg_c,
-            np.ascontiguousarray(dx, dtype=np.int32),
-            np.ascontiguousarray(dy, dtype=np.int32),
-            np.ascontiguousarray(bins, dtype=np.int8),
-            np.uint8(bit_active),
-            np.ascontiguousarray(bg, dtype=np.float32),
         )
-    # Fallback: chiamate separate
+    # Fallback: chiamate separate (stride ignorato in fallback)
     score = score_bitmap(spread, dx, dy, bins, bit_active)
     out = (score - bg) / (1.0 - bg + 1e-6)
     return np.maximum(0.0, out).astype(np.float32)
 
 
-def score_bitmap_greedy(
-    spread: np.ndarray, dx: np.ndarray, dy: np.ndarray, bins: np.ndarray,
-    bit_active: int, min_score: float, greediness: float,
-) -> np.ndarray:
-    """Score bitmap con early-exit greedy. Per coarse-pass aggressivo.
-
-    Non applica rescore background: usare quando la scena ha basso clutter
-    o quando si vuole mass-prune varianti via top-level rapidamente.
-    """
-    if HAS_NUMBA and len(dx) > 0:
-        return _jit_score_bitmap_greedy(
-            np.ascontiguousarray(spread, dtype=np.uint8),
-            np.ascontiguousarray(dx, dtype=np.int32),
-            np.ascontiguousarray(dy, dtype=np.int32),
-            np.ascontiguousarray(bins, dtype=np.int8),
-            np.uint8(bit_active),
-            np.float32(min_score), np.float32(greediness),
-        )
-    # Fallback: kernel base senza early-exit
-    return score_bitmap(spread, dx, dy, bins, bit_active)
-
-
 def popcount_density(spread: np.ndarray) -> np.ndarray:
     if HAS_NUMBA:
         return _jit_popcount_density(np.ascontiguousarray(spread, dtype=np.uint8))

pm2d/line_matcher.py

@@ -40,7 +40,6 @@ from pm2d._jit_kernels import (
     score_by_shift as _jit_score_by_shift,
     score_bitmap as _jit_score_bitmap,
     score_bitmap_rescored as _jit_score_bitmap_rescored,
-    score_bitmap_greedy as _jit_score_bitmap_greedy,
     popcount_density as _jit_popcount,
     HAS_NUMBA,
 )
@@ -574,8 +573,8 @@ class LineShapeMatcher:
         verify_ncc: bool = True,
         verify_threshold: float = 0.4,
         coarse_angle_factor: int = 2,
+        coarse_stride: int = 1,
         scale_penalty: float = 0.0,
-        greediness: float = 0.0,
     ) -> list[Match]:
         """
         scale_penalty: se > 0, riduce lo score per match a scala diversa da 1.0:
@@ -648,23 +647,16 @@ class LineShapeMatcher:
                 neighbor_map[vi_c] = vi_sorted[start:end]
 
         # Pruning varianti via top-level (parallelizzato) - solo coarse.
-        # greediness > 0: usa kernel greedy con early-exit (no rescore bg)
+        # coarse_stride > 1: valuta solo 1 pixel ogni stride, ~stride² speed-up.
-        # per il pruning. ~2-4x speed-up sul top con greediness=0.8.
+        cs = max(1, int(coarse_stride))
-        use_greedy_top = greediness > 0.0
 
         def _top_score(vi: int) -> tuple[int, float]:
             var = self.variants[vi]
             lvl = var.levels[min(top, len(var.levels) - 1)]
-            if use_greedy_top:
+            score = _jit_score_bitmap_rescored(
-                score = _jit_score_bitmap_greedy(
+                spread_top, lvl.dx, lvl.dy, lvl.bin, bit_active_top,
-                    spread_top, lvl.dx, lvl.dy, lvl.bin, bit_active_top,
+                bg_cache_top[var.scale], stride=cs,
-                    top_thresh, greediness,
+            )
-                )
-            else:
-                score = _jit_score_bitmap_rescored(
-                    spread_top, lvl.dx, lvl.dy, lvl.bin, bit_active_top,
-                    bg_cache_top[var.scale],
-                )
             return vi, float(score.max()) if score.size else -1.0
 
         kept_coarse: list[tuple[int, float]] = []