diff --git a/src/arcaea_offline_ocr/crop.py b/src/arcaea_offline_ocr/crop.py
index efc816b..59b663f 100644
--- a/src/arcaea_offline_ocr/crop.py
+++ b/src/arcaea_offline_ocr/crop.py
@@ -5,7 +5,7 @@ import numpy as np
 
 from .types import Mat
 
-__all__ = ["crop_xywh", "crop_black_edges"]
+__all__ = ["crop_xywh", "crop_black_edges", "crop_black_edges_grayscale"]
 
 
 def crop_xywh(mat: Mat, rect: Tuple[int, int, int, int]):
@@ -56,3 +56,51 @@ def crop_black_edges(screenshot: Mat):
         bottom -= 1
 
     return cropped[top:bottom, left:right]
+
+
+def is_black_edge_grayscale(
+    gray_value_list: np.ndarray, black_threshold: int = 50, ratio: float = 0.6
+) -> bool:
+    return (
+        np.count_nonzero(gray_value_list < black_threshold)
+        > len(gray_value_list) * ratio
+    )
+
+
+def crop_black_edges_grayscale(
+    img_gray: Mat, black_threshold: int = 50
+) -> Tuple[int, int, int, int]:
+    """Returns cropped rect"""
+    height, width = img_gray.shape[:2]
+    left = 0
+    right = width
+    top = 0
+    bottom = height
+
+    for i in range(width):
+        column = img_gray[:, i]
+        if not is_black_edge_grayscale(column, black_threshold):
+            break
+        left += 1
+
+    for i in sorted(range(width), reverse=True):
+        column = img_gray[:, i]
+        if i <= left + 1 or not is_black_edge_grayscale(column, black_threshold):
+            break
+        right -= 1
+
+    for i in range(height):
+        row = img_gray[i]
+        if not is_black_edge_grayscale(row, black_threshold):
+            break
+        top += 1
+
+    for i in sorted(range(height), reverse=True):
+        row = img_gray[i]
+        if i <= top + 1 or not is_black_edge_grayscale(row, black_threshold):
+            break
+        bottom -= 1
+
+    assert right > left, "cropped width > 0"
+    assert bottom > top, "cropped height > 0"
+    return (left, top, right - left, bottom - top)