diff --git a/src/RawHandler/RawHandlerRawpy.py b/src/RawHandler/RawHandlerRawpy.py
index 7b3854d..3bbe9c2 100644
--- a/src/RawHandler/RawHandlerRawpy.py
+++ b/src/RawHandler/RawHandlerRawpy.py
@@ -134,20 +134,30 @@ def apply_colorspace_transform(
     def compute_mask_and_sparse(
         self, dims=None, safe_crop=0, divide_by_wl=True
     ) -> Tuple[np.ndarray, np.ndarray]:
-        sparse, mask = sparse_representation_and_mask(
-            self.rawpy_object.raw_image_visible, self.core_metadata.raw_pattern
-        )
-        if divide_by_wl:
-            sparse = sparse / self.core_metadata.white_level
+        raw_img = self.rawpy_object.raw_image_visible
+
         if dims is not None:
             h1, h2, w1, w2 = dims
             if safe_crop:
-                h1, h2, w1, w2 = list(
-                    map(lambda x: x - x % safe_crop, [h1, h2, w1, w2])
-                )
-            return sparse[:, h1:h2, w1:w2], mask[:, h1:h2, w1:w2]
-        else:
-            return sparse, mask
+                # Replaced lambda/map with bitwise/integer math for speed
+                h1 -= h1 % safe_crop
+                h2 -= h2 % safe_crop
+                w1 -= w1 % safe_crop
+                w2 -= w2 % safe_crop
+            raw_img = raw_img[h1:h2, w1:w2]
+            # Roll the pattern to align with crop
+            pattern = np.roll(
+                self.core_metadata.raw_pattern, shift=(-h1, -w1), axis=(0, 1)
+            )
+        # Compute sparse representation on the (potentially smaller) image
+        sparse, mask = sparse_representation_and_mask(raw_img, pattern)
+
+        # Scale by white level
+        if divide_by_wl:
+            # Multiply by reciprocal is often faster than division
+            sparse = sparse * (1.0 / self.core_metadata.white_level)
+
+        return sparse, mask
 
     def downsize(
         self, min_preview_size=256, colorspace=None, clip=False, safe_crop=0
diff --git a/src/RawHandler/utils.py b/src/RawHandler/utils.py
index 5e9fe7a..6e5c4f5 100644
--- a/src/RawHandler/utils.py
+++ b/src/RawHandler/utils.py
@@ -346,16 +346,20 @@ def sparse_representation(cfa, pattern="RGGB", cfa_type="bayer"):
 
 def sparse_representation_and_mask(cfa, pattern):
     H, W = cfa.shape
+    ph, pw = pattern.shape
+    # If two green channels, set both to 1
+    pattern[pattern == 3] = 1
+    # Create the output arrays
     sparse = np.zeros((3, H, W), dtype=cfa.dtype)
-    mask = np.zeros((3, H, W), dtype=int)
-    pattern_shape = pattern.shape
-    for i in range(pattern_shape[0]):
-        for j in range(pattern_shape[1]):
-            ch = pattern[i, j]
-            if ch == 3:
-                ch = 1
-            sparse[ch, i :: pattern_shape[0], j :: pattern_shape[1]] = cfa[
-                i :: pattern_shape[0], j :: pattern_shape[1]
-            ]
-            mask[ch, i :: pattern_shape[0], j :: pattern_shape[1]] = 1
+    mask = np.zeros((3, H, W), dtype=np.uint8)
+
+    # Tile the pattern to match the CFA shape
+    full_pattern = np.tile(pattern, (H // ph + 1, W // pw + 1))
+    full_pattern = full_pattern[:H, :W]
+
+    # Vectorized assignment for each channel (R, G, B)
+    for ch in range(3):
+        ch_mask = full_pattern == ch
+        mask[ch] = ch_mask
+        sparse[ch] = cfa * ch_mask
     return sparse, mask