Fix: Saving images in CMYK mode as RGBA

CHANGELOG.md

@@ -25,6 +25,7 @@ All notable changes to this project will be documented in this file.
 
 - (Heif) `convert_to` should do nothing if the target `mode` is already the current image mode.
 - (AvifImagePlugin) do not register or accept `.avifs` files, libheif does not support them.
+- Images in `CMYK` mode will be converted for `RGBA` mode during saving instead of throwing `KeyError` exception.
 
 ## [0.7.0 - 2022-09-11]
 

docs/image-modes.rst

@@ -45,6 +45,7 @@ When saving image from `Pillow` to `HEIF` format, next modes will be converted a
     * ``P`` will be converted to ``RGB``
     * ``I`` will be converted to ``I;16L``
     * ``1`` will be converted to ``L``
+    * ``CMYK`` will be converted to ``RGBA``
 
 .. _convert_to:
 

pillow_heif/heif.py

@@ -617,6 +617,8 @@ def __add_frame_from_pillow(self, frame: Image.Image, ignore_primary: bool, **kw
             frame = frame.convert(mode="I;16L")
         elif frame.mode == "1":
             frame = frame.convert(mode="L")
+        elif frame.mode == "CMYK":
+            frame = frame.convert(mode="RGBA")
 
         if original_orientation is not None and original_orientation != 1:
             frame = ImageOps.exif_transpose(frame)

tests/write_test.py

@@ -264,13 +264,24 @@ def test_LA_color_mode(save_format):  # noqa
 def test_1_color_mode():
     im = Image.linear_gradient(mode="L")
     im = im.convert(mode="1")
+    assert im.mode == "1"
     out_heif = BytesIO()
     im.save(out_heif, format="HEIF", quality=-1)
     im_heif = Image.open(out_heif)
     assert im_heif.mode == "RGB"
     helpers.compare_hashes([im, im_heif], hash_size=8)
 
 
+def test_CMYK_color_mode():  # noqa
+    im = helpers.gradient_rgba().convert("CMYK")
+    assert im.mode == "CMYK"
+    out_heif = BytesIO()
+    im.save(out_heif, format="HEIF", quality=-1)
+    im_heif = Image.open(out_heif)
+    assert im_heif.mode == "RGBA"
+    helpers.compare_hashes([im, im_heif], hash_size=8)
+
+
 @pytest.mark.parametrize("enc_bits", (10, 12))
 @pytest.mark.parametrize("save_format", ("HEIF", "AVIF"))
 def test_I_color_modes_to_10_12_bit(enc_bits, save_format):  # noqa