diff --git a/sahi/slicing.py b/sahi/slicing.py
index ebeeba4b7..a8c1d7d91 100644
--- a/sahi/slicing.py
+++ b/sahi/slicing.py
@@ -120,7 +120,9 @@ def annotation_inside_slice(annotation: Dict, slice_bbox: List[int]) -> bool:
     return True
 
 
-def process_coco_annotations(coco_annotation_list: List[CocoAnnotation], slice_bbox: List[int], min_area_ratio) -> bool:
+def process_coco_annotations(
+    coco_annotation_list: List[CocoAnnotation], slice_bbox: List[int], min_area_ratio
+) -> List[CocoAnnotation]:
     """Slices and filters given list of CocoAnnotation objects with given
     'slice_bbox' and 'min_area_ratio'.
 
@@ -161,19 +163,19 @@ def __init__(self, image, coco_image, starting_pixel):
 
 
 class SliceImageResult:
-    def __init__(self, original_image_size=None, image_dir: str = None):
+    def __init__(self, original_image_size: List[int], image_dir: Optional[str] = None):
         """
-        sliced_image_list: list of SlicedImage
         image_dir: str
             Directory of the sliced image exports.
         original_image_size: list of int
             Size of the unsliced original image in [height, width]
         """
-        self._sliced_image_list: List[SlicedImage] = []
         self.original_image_height = original_image_size[0]
         self.original_image_width = original_image_size[1]
         self.image_dir = image_dir
 
+        self._sliced_image_list: List[SlicedImage] = []
+
     def add_sliced_image(self, sliced_image: SlicedImage):
         if not isinstance(sliced_image, SlicedImage):
             raise TypeError("sliced_image must be a SlicedImage instance")
@@ -261,13 +263,13 @@ def __len__(self):
 
 def slice_image(
     image: Union[str, Image.Image],
-    coco_annotation_list: Optional[CocoAnnotation] = None,
+    coco_annotation_list: Optional[List[CocoAnnotation]] = None,
     output_file_name: Optional[str] = None,
     output_dir: Optional[str] = None,
-    slice_height: int = None,
-    slice_width: int = None,
-    overlap_height_ratio: float = None,
-    overlap_width_ratio: float = None,
+    slice_height: Optional[int] = None,
+    slice_width: Optional[int] = None,
+    overlap_height_ratio: float = 0.2,
+    overlap_width_ratio: float = 0.2,
     auto_slice_resolution: bool = True,
     min_area_ratio: float = 0.1,
     out_ext: Optional[str] = None,
@@ -278,12 +280,12 @@ def slice_image(
 
     Args:
         image (str or PIL.Image): File path of image or Pillow Image to be sliced.
-        coco_annotation_list (CocoAnnotation): List of CocoAnnotation objects.
+        coco_annotation_list (List[CocoAnnotation], optional): List of CocoAnnotation objects.
         output_file_name (str, optional): Root name of output files (coordinates will
             be appended to this)
         output_dir (str, optional): Output directory
-        slice_height (int): Height of each slice. Default 512.
-        slice_width (int): Width of each slice. Default 512.
+        slice_height (int, optional): Height of each slice. Default None.
+        slice_width (int, optional): Width of each slice. Default None.
         overlap_height_ratio (float): Fractional overlap in height of each
             slice (e.g. an overlap of 0.2 for a slice of size 100 yields an
             overlap of 20 pixels). Default 0.2.
@@ -342,7 +344,6 @@ def _export_single_slice(image: np.ndarray, output_dir: str, slice_file_name: st
         overlap_width_ratio=overlap_width_ratio,
     )
 
-    t0 = time.time()
     n_ims = 0
 
     # init images and annotations lists
@@ -360,23 +361,18 @@ def _export_single_slice(image: np.ndarray, output_dir: str, slice_file_name: st
         bry = slice_bbox[3]
         image_pil_slice = image_pil_arr[tly:bry, tlx:brx]
 
-        # process annotations if coco_annotations is given
-        if coco_annotation_list is not None:
-            sliced_coco_annotation_list = process_coco_annotations(coco_annotation_list, slice_bbox, min_area_ratio)
-
         # set image file suffixes
         slice_suffixes = "_".join(map(str, slice_bbox))
         if out_ext:
             suffix = out_ext
-        else:
-            try:
-                suffix = Path(image_pil.filename).suffix
-                if suffix in IMAGE_EXTENSIONS_LOSSY:
-                    suffix = ".png"
-                elif suffix in IMAGE_EXTENSIONS_LOSSLESS:
-                    suffix = Path(image_pil.filename).suffix
-            except AttributeError:
+        elif hasattr(image_pil, "filename"):
+            suffix = Path(getattr(image_pil, "filename")).suffix
+            if suffix in IMAGE_EXTENSIONS_LOSSY:
                 suffix = ".png"
+            elif suffix in IMAGE_EXTENSIONS_LOSSLESS:
+                suffix = Path(image_pil.filename).suffix
+        else:
+            suffix = ".png"
 
         # set image file name and path
         slice_file_name = f"{output_file_name}_{slice_suffixes}{suffix}"
@@ -387,9 +383,9 @@ def _export_single_slice(image: np.ndarray, output_dir: str, slice_file_name: st
         coco_image = CocoImage(file_name=slice_file_name, height=slice_height, width=slice_width)
 
         # append coco annotations (if present) to coco image
-        if coco_annotation_list:
-            for coco_annotation in sliced_coco_annotation_list:
-                coco_image.add_annotation(coco_annotation)
+        if coco_annotation_list is not None:
+            for sliced_coco_annotation in process_coco_annotations(coco_annotation_list, slice_bbox, min_area_ratio):
+                coco_image.add_annotation(sliced_coco_annotation)
 
         # create sliced image and append to sliced_image_result
         sliced_image = SlicedImage(