diff --git a/pre_commit_images/optimizer.py b/pre_commit_images/optimizer.py
index b76a9f3..d6c72e9 100644
--- a/pre_commit_images/optimizer.py
+++ b/pre_commit_images/optimizer.py
@@ -2,39 +2,40 @@
 from collections.abc import Callable
 from collections.abc import Iterable
 from pathlib import Path
-from tempfile import TemporaryFile
+from tempfile import SpooledTemporaryFile
 from typing import IO
 
 
-def _optimize_images(images: Iterable[str], optimizer_fn: Callable[[Path, IO[bytes]], None], threshold: int) -> bool:
-    def bytes_to_readable(file_size: int) -> str:
-        if file_size / (1024 * 1024) > 1:
-            return f"{file_size / (1024 * 1024):.2f}Mb"
+def _bytes_to_readable(file_size: int) -> str:
+    if file_size / (1024 * 1024) > 1:
+        return f"{file_size / (1024 * 1024):.2f}Mb"
 
-        if file_size / (1024) > 1:
-            return f"{(file_size/1024):.2f}Kb"
+    if file_size / (1024) > 1:
+        return f"{(file_size/1024):.2f}Kb"
 
-        return f"{file_size}b"
+    return f"{file_size}b"
 
-    def optimize_single_image(source: Path, temp: IO[bytes]) -> None:
-        optimizer_fn(source, temp)
 
+def _optimize_images(images: Iterable[str], optimizer: Callable[[Path, IO[bytes]], None], threshold: int) -> bool:
+    def keep_smaller_image(source: Path, candidate: IO[bytes]) -> None:
         source_size = source.stat().st_size
-        diff = source_size - temp.tell()
+        diff = source_size - candidate.tell()
 
         if diff > threshold:
-            temp.seek(0)
-            source.write_bytes(temp.read())
+            candidate.seek(0)
+            source.write_bytes(candidate.read())
 
-            readable_diff = bytes_to_readable(diff)
-            readable_size = bytes_to_readable(source_size)
-            print(f"Optimized {str(source)} by {readable_diff} of {readable_size} ({diff/source_size:.2%})")
+            readable_diff = _bytes_to_readable(diff)
+            readable_size = _bytes_to_readable(source_size)
+            print(f"Optimized {source} by {readable_diff} of {readable_size} ({diff/source_size:.2%})")
 
     ret = True
     for image in images:
         try:
-            with TemporaryFile() as temp:
-                optimize_single_image(Path(image), temp)
+            with SpooledTemporaryFile() as temp:
+                image_path = Path(image)
+                optimizer(image_path, temp)
+                keep_smaller_image(image_path, temp)
         except Exception as exc:  # noqa: PERF203
             print(
                 f"Failed optimization for {image} ({exc})",