From 297965ab0253dfa1b49c7eff2507266af366f424 Mon Sep 17 00:00:00 2001
From: AJ Slater <aj@slater.net>
Date: Tue, 28 Apr 2026 15:34:00 -0700
Subject: [PATCH 1/2] Added bit_depth attribute to PngImageFile

---
 Tests/test_file_png.py               | 13 +++++++++++++
 docs/handbook/image-file-formats.rst |  8 ++++++++
 src/PIL/PngImagePlugin.py            |  3 +++
 3 files changed, 24 insertions(+)

diff --git a/Tests/test_file_png.py b/Tests/test_file_png.py
index 8fe2a5eac68..4c7253b3824 100644
--- a/Tests/test_file_png.py
+++ b/Tests/test_file_png.py
@@ -222,6 +222,19 @@ def test_interlace(self) -> None:
 
             im.load()
 
+    @pytest.mark.parametrize(
+        "test_file, expected_bit_depth",
+        (
+            ("Tests/images/hopper.png", 8),
+            ("Tests/images/hopper_bw_500.png", 1),
+            ("Tests/images/tiny.png", 4),
+            ("Tests/images/i_trns.png", 16),
+        ),
+    )
+    def test_bit_depth(self, test_file: str, expected_bit_depth: int) -> None:
+        with Image.open(test_file) as im:
+            assert im.bit_depth == expected_bit_depth
+
     def test_load_transparent_p(self) -> None:
         test_file = "Tests/images/pil123p.png"
         with Image.open(test_file) as im:
diff --git a/docs/handbook/image-file-formats.rst b/docs/handbook/image-file-formats.rst
index a9fd764e613..7449b28e892 100644
--- a/docs/handbook/image-file-formats.rst
+++ b/docs/handbook/image-file-formats.rst
@@ -895,6 +895,14 @@ decompression bombs. Additionally, the total size of all of the text
 chunks is limited to :data:`.PngImagePlugin.MAX_TEXT_MEMORY`, defaulting to
 64MB.
 
+The :py:class:`~PIL.PngImagePlugin.PngImageFile` class also exposes the
+following attribute:
+
+**bit_depth**
+    The per-sample bit depth read from the PNG ``IHDR`` chunk. Valid values
+    depend on the PNG color type and are one of ``1``, ``2``, ``4``, ``8`` or
+    ``16``.
+
 .. _png-saving:
 
 Saving
diff --git a/src/PIL/PngImagePlugin.py b/src/PIL/PngImagePlugin.py
index 76a15bd0dc6..e2edafa0514 100644
--- a/src/PIL/PngImagePlugin.py
+++ b/src/PIL/PngImagePlugin.py
@@ -391,6 +391,7 @@ def __init__(self, fp: IO[bytes]) -> None:
         self.im_text: dict[str, str | iTXt] = {}
         self.im_size = (0, 0)
         self.im_mode = ""
+        self.im_bit_depth = 0
         self.im_tile: list[ImageFile._Tile] = []
         self.im_palette: tuple[str, bytes] | None = None
         self.im_custom_mimetype: str | None = None
@@ -459,6 +460,7 @@ def chunk_IHDR(self, pos: int, length: int) -> bytes:
             msg = "Truncated IHDR chunk"
             raise ValueError(msg)
         self.im_size = i32(s, 0), i32(s, 4)
+        self.im_bit_depth = s[8]
         try:
             self.im_mode, self.im_rawmode = _MODES[(s[8], s[9])]
         except Exception:
@@ -801,6 +803,7 @@ def _open(self) -> None:
         self._mode = self.png.im_mode
         self._size = self.png.im_size
         self.info = self.png.im_info
+        self.bit_depth = self.png.im_bit_depth
         self._text: dict[str, str | iTXt] | None = None
         self.tile = self.png.im_tile
         self.custom_mimetype = self.png.im_custom_mimetype

From eddbdd254da876a1972dd3a23fef2701f9dd9ee1 Mon Sep 17 00:00:00 2001
From: AJ Slater <aj@slater.net>
Date: Fri, 1 May 2026 15:22:31 -0700
Subject: [PATCH 2/2] Narrow Image type for bit_depth assertions to fix mypy

---
 Tests/test_file_png.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Tests/test_file_png.py b/Tests/test_file_png.py
index 4c7253b3824..87493c75ca5 100644
--- a/Tests/test_file_png.py
+++ b/Tests/test_file_png.py
@@ -233,6 +233,7 @@ def test_interlace(self) -> None:
     )
     def test_bit_depth(self, test_file: str, expected_bit_depth: int) -> None:
         with Image.open(test_file) as im:
+            assert isinstance(im, PngImagePlugin.PngImageFile)
             assert im.bit_depth == expected_bit_depth
 
     def test_load_transparent_p(self) -> None: