Support saving CMYK JP2 images

Tests/test_file_jpeg2k.py

@@ -325,6 +325,18 @@ def test_cmyk() -> None:
         assert im.getpixel((0, 0)) == (185, 134, 0, 0)
 
 
+@pytest.mark.skipif(
+    not os.path.exists(EXTRA_DIR), reason="Extra image files not installed"
+)
+@skip_unless_feature_version("jpg_2000", "2.5.3")
+def test_cmyk_save() -> None:
+    with Image.open(f"{EXTRA_DIR}/issue205.jp2") as jp2:
+        assert jp2.mode == "CMYK"
+
+        im = roundtrip(jp2)
+        assert_image_equal(im, jp2)
+
+
 @pytest.mark.parametrize("ext", (".j2k", ".jp2"))
 def test_16bit_monochrome_has_correct_mode(ext: str) -> None:
     with Image.open("Tests/images/16bit.cropped" + ext) as im:

docs/handbook/image-file-formats.rst

@@ -573,9 +573,11 @@ Pillow reads and writes JPEG 2000 files containing ``L``, ``LA``, ``RGB``,
 ``RGBA``, or ``YCbCr`` data.  When reading, ``YCbCr`` data is converted to
 ``RGB`` or ``RGBA`` depending on whether or not there is an alpha channel.
 Beginning with version 8.3.0, Pillow can read (but not write) ``RGB``,
-``RGBA``, and ``YCbCr`` images with subsampled components.  Pillow supports
-JPEG 2000 raw codestreams (``.j2k`` files), as well as boxed JPEG 2000 files
-(``.jp2`` or ``.jpx`` files).
+``RGBA``, and ``YCbCr`` images with subsampled components. Pillow 10.4.0 and
+later can read ``CMYK`` images with OpenJPEG 2.5.1 and later, and Pillow 11.1.0
+and later can write ``CMYK`` images with OpenJPEG 2.5.3 and later. Pillow
+supports JPEG 2000 raw codestreams (``.j2k`` files), as well as boxed JPEG 2000
+files (``.jp2`` or ``.jpx`` files).
 
 When loading, if you set the ``mode`` on the image prior to the
 :py:meth:`~PIL.Image.Image.load` method being invoked, you can ask Pillow to

docs/releasenotes/11.1.0.rst

@@ -52,6 +52,11 @@ zlib library, and what version of zlib-ng is being used::
 Other Changes
 =============
 
+Saving JPEG 2000 CMYK images
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+With OpenJPEG 2.5.3 or later, Pillow can now save CMYK images as JPEG 2000 files.
+
 zlib-ng in wheels
 ^^^^^^^^^^^^^^^^^
 

src/libImaging/Jpeg2KEncode.c

@@ -330,6 +330,13 @@ j2k_encode_entry(Imaging im, ImagingCodecState state) {
         components = 4;
         color_space = OPJ_CLRSPC_SRGB;
         pack = j2k_pack_rgba;
+#if ((OPJ_VERSION_MAJOR == 2 && OPJ_VERSION_MINOR == 5 && OPJ_VERSION_BUILD >= 3) || \
+     (OPJ_VERSION_MAJOR == 2 && OPJ_VERSION_MINOR > 5) || OPJ_VERSION_MAJOR > 2)
+    } else if (strcmp(im->mode, "CMYK") == 0) {
+        components = 4;
+        color_space = OPJ_CLRSPC_CMYK;
+        pack = j2k_pack_rgba;
+#endif
     } else {
         state->errcode = IMAGING_CODEC_BROKEN;
         state->state = J2K_STATE_FAILED;