From d5d0734169ac4c593caac4f5769e60a01574fa09 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Mon, 16 Mar 2026 20:48:25 +1100
Subject: [PATCH] Add CMYK palettes

---
 Tests/test_image_putpalette.py | 15 +++++++++++++++
 src/PIL/Image.py               | 11 ++++++++---
 src/libImaging/Pack.c          | 14 ++++++++++++++
 src/libImaging/Palette.c       |  3 ++-
 4 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/Tests/test_image_putpalette.py b/Tests/test_image_putpalette.py
index 661764b60..237de6330 100644
--- a/Tests/test_image_putpalette.py
+++ b/Tests/test_image_putpalette.py
@@ -91,6 +91,21 @@ def test_rgba_palette(mode: str, palette: tuple[int, ...]) -> None:
     assert im.palette.colors == {(1, 2, 3, 4): 0}
 
 
+@pytest.mark.parametrize(
+    "mode, palette",
+    (
+        ("CMYK", (1, 2, 3, 4)),
+        ("CMYKX", (1, 2, 3, 4, 0)),
+    ),
+)
+def test_cmyk_palette(mode: str, palette: tuple[int, ...]) -> None:
+    im = Image.new("P", (1, 1))
+    im.putpalette(palette, mode)
+    assert im.getpalette() == [250, 249, 248]
+    assert im.palette is not None
+    assert im.palette.colors == {(1, 2, 3, 4): 0}
+
+
 def test_empty_palette() -> None:
     im = Image.new("P", (1, 1))
     assert im.getpalette() == []
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index cc431a86a..c9db97319 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -2145,8 +2145,8 @@ class Image:
         Alternatively, an 8-bit string may be used instead of an integer sequence.
 
         :param data: A palette sequence (either a list or a string).
-        :param rawmode: The raw mode of the palette. Either "RGB", "RGBA", or a mode
-           that can be transformed to "RGB" or "RGBA" (e.g. "R", "BGR;15", "RGBA;L").
+        :param rawmode: The raw mode of the palette. Either "RGB", "RGBA", "CMYK", or a
+           mode that can be transformed to one of those modes (e.g. "R", "RGBA;L").
         """
         from . import ImagePalette
 
@@ -2165,7 +2165,12 @@ class Image:
             palette = ImagePalette.raw(rawmode, data)
         self._mode = "PA" if "A" in self.mode else "P"
         self.palette = palette
-        self.palette.mode = "RGBA" if "A" in rawmode else "RGB"
+        if rawmode.startswith("CMYK"):
+            self.palette.mode = "CMYK"
+        elif "A" in rawmode:
+            self.palette.mode = "RGBA"
+        else:
+            self.palette.mode = "RGB"
         self.load()  # install new palette
 
     def putpixel(
diff --git a/src/libImaging/Pack.c b/src/libImaging/Pack.c
index fdf5a72aa..161d82f2e 100644
--- a/src/libImaging/Pack.c
+++ b/src/libImaging/Pack.c
@@ -325,6 +325,19 @@ ImagingPackXBGR(UINT8 *out, const UINT8 *in, int pixels) {
     }
 }
 
+void
+ImagingPackCMYK2RGB(UINT8 *out, const UINT8 *in, int xsize) {
+    int x, nk, tmp;
+    for (x = 0; x < xsize; x++) {
+        nk = 255 - in[3];
+        out[0] = CLIP8(nk - MULDIV255(in[0], nk, tmp));
+        out[1] = CLIP8(nk - MULDIV255(in[1], nk, tmp));
+        out[2] = CLIP8(nk - MULDIV255(in[2], nk, tmp));
+        out += 3;
+        in += 4;
+    }
+}
+
 void
 ImagingPackBGRA(UINT8 *out, const UINT8 *in, int pixels) {
     int i;
@@ -605,6 +618,7 @@ static struct {
     {IMAGING_MODE_CMYK, IMAGING_RAWMODE_M, 8, band1},
     {IMAGING_MODE_CMYK, IMAGING_RAWMODE_Y, 8, band2},
     {IMAGING_MODE_CMYK, IMAGING_RAWMODE_K, 8, band3},
+    {IMAGING_MODE_CMYK, IMAGING_RAWMODE_RGB, 24, ImagingPackCMYK2RGB},
 
     /* video (YCbCr) */
     {IMAGING_MODE_YCbCr, IMAGING_RAWMODE_YCbCr, 24, ImagingPackRGB},
diff --git a/src/libImaging/Palette.c b/src/libImaging/Palette.c
index 371ba644b..b2dacf656 100644
--- a/src/libImaging/Palette.c
+++ b/src/libImaging/Palette.c
@@ -27,7 +27,8 @@ ImagingPaletteNew(const ModeID mode) {
     int i;
     ImagingPalette palette;
 
-    if (mode != IMAGING_MODE_RGB && mode != IMAGING_MODE_RGBA) {
+    if (mode != IMAGING_MODE_RGB && mode != IMAGING_MODE_RGBA &&
+        mode != IMAGING_MODE_CMYK) {
         return (ImagingPalette)ImagingError_ModeError();
     }