From 1a36f70ff9e1ab7c6a480cdd01f2248f0efa97ee Mon Sep 17 00:00:00 2001
From: qodelicious <162776175+qodelicious@users.noreply.github.com>
Date: Wed, 21 Oct 2026 00:21:21 +0000
Subject: [PATCH 1/3] Fix saving L images as Palm

Since the colormap change in #8685, an L image saved with bpp went through the P mode branch because its mode is switched to P before writing, and failed with 'image has no palette'. Only write the custom colormap for real P images. Also document the bpp option.
---
 Tests/test_file_palm.py              | 33 ++++++++++++++++++++++++++++
 docs/handbook/image-file-formats.rst | 14 ++++++++++++
 src/PIL/PalmImagePlugin.py           |  2 +-
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/Tests/test_file_palm.py b/Tests/test_file_palm.py
index ffac42e889d..3753520aa1d 100644
--- a/Tests/test_file_palm.py
+++ b/Tests/test_file_palm.py
@@ -2,6 +2,7 @@
 
 import os.path
 import subprocess
+from io import BytesIO
 
 import pytest
 
@@ -72,6 +73,38 @@ def test_p_mode(tmp_path: Path) -> None:
     roundtrip(tmp_path, mode)
 
 
+@pytest.mark.parametrize("bpp", (1, 2, 4))
+def test_l_mode(bpp: int) -> None:
+    im = Image.new("L", (4, 1))
+    im.putdata([0, 85, 170, 255])
+
+    out = BytesIO()
+    im.save(out, "PALM", bpp=bpp)
+
+    data = out.getvalue()
+    # No custom colormap flag, and the requested bits per pixel
+    assert data[6:8] == b"\x00\x00"
+    assert data[8] == bpp
+    assert len(data) == 16 + 2
+
+    # Palm grayscale goes from white (0) to black
+    expected = {1: b"\xc0\x00", 2: b"\xe4\x00", 4: b"\xfa\x50"}
+    assert data[16:] == expected[bpp]
+
+
+def test_l_mode_info_bpp() -> None:
+    im = Image.new("L", (4, 1))
+    im.putdata([0, 1, 2, 3])
+    im.info["bpp"] = 2
+
+    out = BytesIO()
+    im.save(out, "PALM")
+
+    data = out.getvalue()
+    assert data[8] == 2
+    assert data[16:] == b"\xe4\x00"
+
+
 @pytest.mark.parametrize("mode", ("L", "RGB"))
 def test_oserror(tmp_path: Path, mode: str) -> None:
     with pytest.raises(OSError):
diff --git a/docs/handbook/image-file-formats.rst b/docs/handbook/image-file-formats.rst
index 1cc01838909..c650a799308 100644
--- a/docs/handbook/image-file-formats.rst
+++ b/docs/handbook/image-file-formats.rst
@@ -1788,6 +1788,20 @@ Pillow provides write-only support for PALM pixmap files.
 
 The format code is ``Palm``, the extension is ``.palm``.
 
+``1``, ``L`` and ``P`` images can be saved.
+
+Saving
+~~~~~~
+
+The :py:meth:`~PIL.Image.Image.save` method can take the following keyword arguments:
+
+**bpp**
+    For ``L`` images, the number of bits per pixel to write, either 1, 2 or 4.
+    The image is reduced to that many shades of gray. If it is not given, the
+    ``bpp`` value from :py:attr:`~PIL.Image.Image.info` is used instead, and
+    only the lowest bits of each pixel are kept. ``L`` images cannot be saved
+    without one of these.
+
 PDF
 ^^^
 
diff --git a/src/PIL/PalmImagePlugin.py b/src/PIL/PalmImagePlugin.py
index bf8e81a5f5e..80efa6e032f 100644
--- a/src/PIL/PalmImagePlugin.py
+++ b/src/PIL/PalmImagePlugin.py
@@ -172,7 +172,7 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     compression_type = _COMPRESSION_TYPES["none"]
 
     flags = 0
-    if im.mode == "P":
+    if rawmode == "P":
         flags |= _FLAGS["custom-colormap"]
         colormap = im.im.getpalette()
         colors = len(colormap) // 3

From fb7397622e4245c4e58a7ba9ebb3fa2c5b389af0 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Wed, 21 Oct 2026 12:21:57 +1100
Subject: [PATCH 2/3] Do not change original image mode

---
 src/PIL/PalmImagePlugin.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/PIL/PalmImagePlugin.py b/src/PIL/PalmImagePlugin.py
index 80efa6e032f..8e8a92e944c 100644
--- a/src/PIL/PalmImagePlugin.py
+++ b/src/PIL/PalmImagePlugin.py
@@ -144,8 +144,7 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
             raise OSError(msg)
 
         # we ignore the palette here
-        im._mode = "P"
-        rawmode = f"P;{bpp}"
+        rawmode = f"L;{bpp}"
         version = 1
 
     elif im.mode == "1":
@@ -172,7 +171,7 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     compression_type = _COMPRESSION_TYPES["none"]
 
     flags = 0
-    if rawmode == "P":
+    if im.mode == "P":
         flags |= _FLAGS["custom-colormap"]
         colormap = im.im.getpalette()
         colors = len(colormap) // 3

From 16ab90286e23202db9ffcefe6daa09c3ff5a74aa Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Wed, 21 Oct 2026 13:05:22 +1100
Subject: [PATCH 3/3] Test image similarity, rather than specific bytes

---
 Tests/test_file_palm.py              | 78 ++++++++++------------------
 docs/handbook/image-file-formats.rst | 10 ++--
 src/PIL/PalmImagePlugin.py           |  1 -
 3 files changed, 32 insertions(+), 57 deletions(-)

diff --git a/Tests/test_file_palm.py b/Tests/test_file_palm.py
index 3753520aa1d..f43a9ee2cff 100644
--- a/Tests/test_file_palm.py
+++ b/Tests/test_file_palm.py
@@ -2,17 +2,17 @@
 
 import os.path
 import subprocess
-from io import BytesIO
 
 import pytest
 
 from PIL import Image
 
-from .helper import assert_image_equal, hopper, magick_command
+from .helper import assert_image_equal, assert_image_similar, hopper, magick_command
 
 TYPE_CHECKING = False
 if TYPE_CHECKING:
     from pathlib import Path
+    from typing import Any
 
 
 def helper_save_as_palm(tmp_path: Path, mode: str) -> None:
@@ -37,72 +37,48 @@ def open_with_magick(magick: list[str], tmp_path: Path, f: str) -> Image.Image:
     return Image.open(outfile)
 
 
-def roundtrip(tmp_path: Path, mode: str) -> None:
+def roundtrip(tmp_path: Path, im: Image.Image, **options: Any) -> Image.Image:
     magick = magick_command()
     if not magick:
         pytest.skip("ImageMagick not available")
 
-    im = hopper(mode)
     outfile = str(tmp_path / "temp.palm")
 
-    im.save(outfile)
-    converted = open_with_magick(magick, tmp_path, outfile)
-    if mode == "P":
-        assert converted.mode == "P"
-
-        im = im.convert("RGB")
-        converted = converted.convert("RGB")
-    assert_image_equal(converted, im)
+    im.save(outfile, **options)
+    return open_with_magick(magick, tmp_path, outfile)
 
 
 def test_monochrome(tmp_path: Path) -> None:
-    # Arrange
-    mode = "1"
+    helper_save_as_palm(tmp_path, "1")
 
-    # Act / Assert
-    helper_save_as_palm(tmp_path, mode)
-    roundtrip(tmp_path, mode)
+    im = hopper("1")
+    assert_image_equal(roundtrip(tmp_path, im), im)
 
 
 def test_p_mode(tmp_path: Path) -> None:
-    # Arrange
-    mode = "P"
+    helper_save_as_palm(tmp_path, "P")
 
-    # Act / Assert
-    helper_save_as_palm(tmp_path, mode)
-    roundtrip(tmp_path, mode)
+    im = hopper("P")
+    converted = roundtrip(tmp_path, im)
+    assert converted.mode == "P"
+    assert_image_equal(converted.convert("RGB"), im.convert("RGB"))
 
 
 @pytest.mark.parametrize("bpp", (1, 2, 4))
-def test_l_mode(bpp: int) -> None:
-    im = Image.new("L", (4, 1))
-    im.putdata([0, 85, 170, 255])
-
-    out = BytesIO()
-    im.save(out, "PALM", bpp=bpp)
-
-    data = out.getvalue()
-    # No custom colormap flag, and the requested bits per pixel
-    assert data[6:8] == b"\x00\x00"
-    assert data[8] == bpp
-    assert len(data) == 16 + 2
-
-    # Palm grayscale goes from white (0) to black
-    expected = {1: b"\xc0\x00", 2: b"\xe4\x00", 4: b"\xfa\x50"}
-    assert data[16:] == expected[bpp]
-
-
-def test_l_mode_info_bpp() -> None:
-    im = Image.new("L", (4, 1))
-    im.putdata([0, 1, 2, 3])
-    im.info["bpp"] = 2
-
-    out = BytesIO()
-    im.save(out, "PALM")
-
-    data = out.getvalue()
-    assert data[8] == 2
-    assert data[16:] == b"\xe4\x00"
+@pytest.mark.parametrize("info", (True, False))
+def test_l_mode(tmp_path: Path, bpp: int, info: bool) -> None:
+    im = hopper("L")
+    if info:
+        reloaded = roundtrip(tmp_path, im, bpp=bpp)
+    else:
+        im.info["bpp"] = bpp
+        reloaded = roundtrip(tmp_path, im)
+    if bpp == 1:
+        assert reloaded.mode == "1"
+    else:
+        assert reloaded.mode == "L"
+        if info:
+            assert_image_similar(reloaded, im, 23 if bpp == 2 else 6)
 
 
 @pytest.mark.parametrize("mode", ("L", "RGB"))
diff --git a/docs/handbook/image-file-formats.rst b/docs/handbook/image-file-formats.rst
index c650a799308..518bb4faa8e 100644
--- a/docs/handbook/image-file-formats.rst
+++ b/docs/handbook/image-file-formats.rst
@@ -1796,11 +1796,11 @@ Saving
 The :py:meth:`~PIL.Image.Image.save` method can take the following keyword arguments:
 
 **bpp**
-    For ``L`` images, the number of bits per pixel to write, either 1, 2 or 4.
-    The image is reduced to that many shades of gray. If it is not given, the
-    ``bpp`` value from :py:attr:`~PIL.Image.Image.info` is used instead, and
-    only the lowest bits of each pixel are kept. ``L`` images cannot be saved
-    without one of these.
+    For ``L`` images, the number of bits per pixel to write, either 1, 2 or 4. Shades
+    in the image are adjusted to fit within this restriction. If omitted, the ``bpp``
+    value from :py:attr:`~PIL.Image.Image.info` can be used instead, and only the
+    lowest bits of each pixel are kept. If there is no ``bpp`` setting at all, ``L``
+    mode images cannot be saved.
 
 PDF
 ^^^
diff --git a/src/PIL/PalmImagePlugin.py b/src/PIL/PalmImagePlugin.py
index 8e8a92e944c..8b4473892f0 100644
--- a/src/PIL/PalmImagePlugin.py
+++ b/src/PIL/PalmImagePlugin.py
@@ -143,7 +143,6 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
             msg = f"cannot write mode {im.mode} as Palm"
             raise OSError(msg)
 
-        # we ignore the palette here
         rawmode = f"L;{bpp}"
         version = 1