fix(demo): harden mask hole-filling for border-touching cases

opengait/demo/preprocess.py

@@ -64,6 +64,29 @@ def _to_numpy_array(value: object) -> NDArray[np.generic]:
     return cast(NDArray[np.generic], np.asarray(current))
 
 
+def _fill_binary_holes(mask_u8: UInt8Array) -> UInt8Array:
+    mask_bin = np.where(mask_u8 > 0, np.uint8(255), np.uint8(0)).astype(np.uint8)
+    h, w = cast(tuple[int, int], mask_bin.shape)
+    if h <= 2 or w <= 2:
+        return mask_bin
+
+    seed_candidates = [(0, 0), (w - 1, 0), (0, h - 1), (w - 1, h - 1)]
+    seed: tuple[int, int] | None = None
+    for x, y in seed_candidates:
+        if int(mask_bin[y, x]) == 0:
+            seed = (x, y)
+            break
+    if seed is None:
+        return mask_bin
+
+    flood = mask_bin.copy()
+    flood_mask = np.zeros((h + 2, w + 2), dtype=np.uint8)
+    _ = cv2.floodFill(flood, flood_mask, seed, 255)
+    holes = cv2.bitwise_not(flood)
+    filled = cv2.bitwise_or(mask_bin, holes)
+    return cast(UInt8Array, filled)
+
+
 def _bbox_from_mask(mask: UInt8[ndarray, "h w"]) -> BBoxXYXY | None:
     """Extract bounding box from binary mask in XYXY format.
 
@@ -248,6 +271,7 @@ def mask_to_silhouette(
         or None if conversion fails.
     """
     mask_u8 = np.where(mask > 0, np.uint8(255), np.uint8(0)).astype(np.uint8)
+    mask_u8 = _fill_binary_holes(mask_u8)
     if int(np.count_nonzero(mask_u8)) < MIN_MASK_AREA:
         return None