diff --git a/src/image_io.py b/src/image_io.py
index afedda0..e4de01e 100644
--- a/src/image_io.py
+++ b/src/image_io.py
@@ -3,14 +3,14 @@
 from PIL import Image
 import os
 import glob
-from typing import Union, Tuple, Iterator
+from typing import Union, Tuple, Iterator, Optional
 import logging
 
 logger = logging.getLogger("adjust-scan-images")
 
 
 def read_image(
-    path: str, resize_ratio: Union[float, None] = None
+    path: str, resize_ratio: Optional[float] = None
 ) -> Union[Tuple[None, None], Tuple[np.ndarray, Tuple[int, int]]]:
     """
     Read image in grayscale.
@@ -40,7 +40,7 @@ def read_image(
 
 
 def read_images(
-    dirname: str, ext: Union[str, None] = None, resize_ratio: Union[float, None] = None
+    dirname: str, ext: Optional[str] = None, resize_ratio: Optional[float] = None
 ) -> Iterator[Tuple[str, np.ndarray, Tuple[int, int]]]:
     """
     Read images and return iterator.
diff --git a/src/log_setting.py b/src/log_setting.py
index dca5ef1..e7136f7 100644
--- a/src/log_setting.py
+++ b/src/log_setting.py
@@ -1,7 +1,7 @@
 import os
 import logging
 from logging import getLogger, StreamHandler, FileHandler, Formatter
-from typing import Union
+from typing import Optional
 
 from .const import NOW
 
@@ -10,7 +10,7 @@
 
 def set_logger(
     console_mode: int = logging.INFO,
-    logpath: Union[str, None] = None,
+    logpath: Optional[str] = None,
     file_mode: int = logging.WARN,
 ):
     """
diff --git a/src/pipeline.py b/src/pipeline.py
index eac4594..54701eb 100644
--- a/src/pipeline.py
+++ b/src/pipeline.py
@@ -1,6 +1,6 @@
 import os
 import logging
-from typing import Union
+from typing import Optional, List, Tuple
 
 from .setting_io import MarksheetResultWriter
 from .setting_io_ds import read_metadata, read_marksheet_setting, decide_save_filename
@@ -15,7 +15,7 @@
 
 
 def pipeline(
-    img_dir: str, metadata_path: Union[None, str], save_dir: str, baseimg_path: str
+    img_dir: str, metadata_path: Optional[str], save_dir: str, baseimg_path: str
 ):
     """
     Process pipeline.
@@ -42,12 +42,12 @@ def pipeline(
     # metadata = read_metadata(metadata_path, pt2px = dpi[0])
     baseimg, dpi = read_image(baseimg_path)
     metadata = read_metadata(None, pt2px=dpi[0])
-    resize_ratio = metadata["resize_ratio"]
-    is_align = metadata["is_align"]
-    is_marksheet = metadata["is_marksheet"]
-    is_marksheet_fit = metadata["is_marksheet_fit"]
+    resize_ratio: float = metadata["resize_ratio"]
+    is_align: bool = metadata["is_align"]
+    is_marksheet: bool = metadata["is_marksheet"]
+    is_marksheet_fit: bool = metadata["is_marksheet_fit"]
     coord_unit = metadata["coord_unit"]
-    pt2px = dpi[0] if coord_unit == "pt" else None
+    pt2px: Optional[int] = dpi[0] if coord_unit == "pt" else None
 
     # read base image
     logger.debug(f"Begin reading the base image {baseimg_path}")
@@ -65,8 +65,8 @@ def pipeline(
         mark_reader = MarkReader(metadata)
         marksheet_result_path = os.path.join(save_dir, f"marksheet_result_{NOW}.csv")
         logger.info(f"Marksheet result is saved at {marksheet_result_path}")
-        marksheet_result_header = ["origin_filename", "save_filename"] + list(
-            metadata["sheet"].keys()
+        marksheet_result_header = tuple(
+            ["origin_filename", "save_filename"] + list(metadata["sheet"].keys())
         )
         marksheet_result_writer = MarksheetResultWriter(
             marksheet_result_path, marksheet_result_header
@@ -82,7 +82,7 @@ def pipeline(
         mark_reader.fit(baseimg)
 
     img_iter = read_images(img_dir, resize_ratio=resize_ratio)
-    error_paths = []
+    error_paths: List[Tuple[str, str]] = []
     image_saver = ImageSaver(save_dir)
     for p, img, dpi in img_iter:
         is_error = False
diff --git a/src/read_marksheet.py b/src/read_marksheet.py
index 672b7da..110eacc 100644
--- a/src/read_marksheet.py
+++ b/src/read_marksheet.py
@@ -1,7 +1,7 @@
 import numpy as np
 import cv2
 import logging
-from typing import Union
+from typing import Union, Optional
 
 logger = logging.getLogger("adjust-scan-images")
 
@@ -41,7 +41,7 @@ def __init__(self, metadata: dict):
             Image metadata. See Note.
         """
         self.metadata = metadata
-        self.sheet = self.metadata.get("sheet", {})
+        self.sheet: dict = self.metadata.get("sheet", {})
         self.is_sheet = bool(self.sheet)
         self.coord_style = self.metadata.get("sheet_coord_style", "circle")
         if not self.is_sheet:
@@ -52,9 +52,9 @@ def __init__(self, metadata: dict):
         if self.coord_style == "circle":
             self.sheet = self.circle2bbox(self.sheet)
             logger.debug(f"MarkReader: circle -> bbox: {self.sheet}")
-        self.g_ksize = self.metadata.get("sheet_gaussian_ksize", 0)
-        self.g_std = self.metadata.get("sheet_gaussian_std", 0)
-        self.threshold = self.metadata.get("sheet_score_threshold", 0)
+        self.g_ksize: int = self.metadata.get("sheet_gaussian_ksize", 0)
+        self.g_std: int = self.metadata.get("sheet_gaussian_std", 0)
+        self.threshold: int = self.metadata.get("sheet_score_threshold", 0)
         self.is_fitted = False
         self.base_scores = None
 
@@ -124,7 +124,7 @@ def _preprocess(self, img: np.ndarray) -> np.ndarray:
         return preprocessed
 
     def _one_mark_score(
-        self, img: np.ndarray, coords: dict, base_score: Union[dict, None] = None
+        self, img: np.ndarray, coords: dict, base_score: Optional[dict] = None
     ) -> dict:
         """
         Read one mark score.
@@ -153,7 +153,7 @@ def _one_mark_score(
         return scores
 
     def _one_mark(
-        self, img: np.ndarray, coords: dict, base_score: Union[dict, None] = None
+        self, img: np.ndarray, coords: dict, base_score: Optional[dict] = None
     ) -> Union[None, str]:
         """
         Read one category.
diff --git a/src/setting_io.py b/src/setting_io.py
index ded2199..3e414a4 100644
--- a/src/setting_io.py
+++ b/src/setting_io.py
@@ -2,7 +2,7 @@
 from openpyxl import load_workbook
 from collections import defaultdict
 import logging
-from typing import Union, Iterable
+from typing import Iterable, Optional
 
 logger = logging.getLogger("adjust-scan-images")
 
@@ -24,10 +24,10 @@
 
 
 def read_metadata(
-    filepath: Union[None, str] = None,
+    filepath: Optional[str] = None,
     mode: str = "excel",
     excel_sheet_name: str = "image_setting",
-    pt2px: Union[None, float] = None,
+    pt2px: Optional[float] = None,
     *args,
     **kargs,
 ) -> dict:
@@ -36,12 +36,14 @@ def read_metadata(
 
     Parameters
     ----------
-    filepath : str
-        Setting file path.
+    filepath : str | None, optional
+        Setting file path, by default None
     mode : str, optional
         Mode, by default "excel"
     excel_sheet_name : str, optional
         Excel sheet name, by default "image_setting"
+    pt2px : float | None, optional
+        if coord unit is pt, you should set the value dpi, optinal by defalut None
 
     Returns
     -------
diff --git a/src/setting_io_ds.py b/src/setting_io_ds.py
index e3708a0..f367318 100644
--- a/src/setting_io_ds.py
+++ b/src/setting_io_ds.py
@@ -2,7 +2,7 @@
 import os
 from collections import defaultdict
 import logging
-from typing import Union, Iterable
+from typing import Iterable, Optional
 
 logger = logging.getLogger("adjust-scan-images")
 
@@ -25,10 +25,10 @@
 
 
 def read_metadata(
-    filepath: Union[None, str] = None,
+    filepath: Optional[str] = None,
     mode: str = "excel",
     excel_sheet_name: str = "image_setting",
-    pt2px: Union[None, float] = None,
+    pt2px: Optional[float] = None,
     *args,
     **kargs,
 ) -> dict:
@@ -96,10 +96,10 @@ def read_metadata(
 
 
 def read_marksheet_setting(
-    filepath: Union[None, str],
+    filepath: Optional[str],
     scale: float = 1,
-    categories: Union[None, Iterable[str]] = MARK_CATEGORIES,
-    pt2px: Union[None, float] = None,
+    categories: Optional[Iterable[str]] = MARK_CATEGORIES,
+    pt2px: Optional[float] = None,
     *args,
     **kargs,
 ) -> dict:
@@ -150,7 +150,7 @@ def read_marksheet_setting(
 
 
 def decide_save_filename(
-    read_path: str, save_dir: str, data: Union[dict, None] = None
+    read_path: str, save_dir: str, data: Optional[dict] = None
 ) -> str:
     """
     Decide file name when saving an image. OVERRIDE THIS TO CHANGE THE FILENAME.