Support reading JPEG2000 images with CMYK palettes (#9456)

Author: hugovk

Tests/test_file_jpeg2k.py

@@ -445,6 +445,7 @@ def test_pclr() -> None:
     ) as im:
         assert im.mode == "P"
         assert im.palette is not None
+        assert im.palette.mode == "CMYK"
         assert len(im.palette.colors) == 139
         assert im.palette.colors[(0, 0, 0, 0)] == 0
 

Tests/test_file_png.py

@@ -707,6 +707,16 @@ def test_plte_length(self, tmp_path: Path) -> None:
             assert reloaded.png.im_palette is not None
             assert len(reloaded.png.im_palette[1]) == 3
 
+    def test_plte_cmyk(self, tmp_path: Path) -> None:
+        im = Image.new("P", (1, 1))
+        im.putpalette((0, 100, 150, 200), "CMYK")
+
+        out = tmp_path / "temp.png"
+        im.save(out)
+
+        with Image.open(out) as reloaded:
+            assert reloaded.convert("CMYK").getpixel((0, 0)) == (200, 222, 232, 0)
+
     def test_getxmp(self) -> None:
         with Image.open("Tests/images/color_snakes.png") as im:
             if ElementTree is None:

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() == []

src/PIL/Image.py

@@ -2145,8 +2145,8 @@ def putpalette(
         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 @@ def putpalette(
             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(

src/PIL/Jpeg2KImagePlugin.py

@@ -176,6 +176,7 @@ def _parse_jp2_header(
     nc = None
     dpi = None  # 2-tuple of DPI info, or None
     palette = None
+    cmyk = False
 
     while header.has_next_box():
         tbox = header.next_box_type()
@@ -196,10 +197,11 @@ def _parse_jp2_header(
                 mode = "RGB"
             elif nc == 4:
                 mode = "RGBA"
-        elif tbox == b"colr" and nc == 4:
+        elif tbox == b"colr":
             meth, _, _, enumcs = header.read_fields(">BBBI")
-            if meth == 1 and enumcs == 12:
-                mode = "CMYK"
+            if cmyk := (meth == 1 and enumcs == 12):
+                if nc == 4:
+                    mode = "CMYK"
         elif tbox == b"pclr" and mode in ("L", "LA"):
             ne, npc = header.read_fields(">HB")
             assert isinstance(ne, int)
@@ -210,7 +212,11 @@ def _parse_jp2_header(
                 if bitdepth > max_bitdepth:
                     max_bitdepth = bitdepth
             if max_bitdepth <= 8:
-                palette = ImagePalette.ImagePalette("RGBA" if npc == 4 else "RGB")
+                if npc == 4:
+                    palette_mode = "CMYK" if cmyk else "RGBA"
+                else:
+                    palette_mode = "RGB"
+                palette = ImagePalette.ImagePalette(palette_mode)
                 for i in range(ne):
                     color: list[int] = []
                     for value in header.read_fields(">" + ("B" * npc)):

src/PIL/PngImagePlugin.py

@@ -1353,6 +1353,9 @@ def _save(
         mode = im.mode
 
     outmode = mode
+    palette = []
+    if im.palette:
+        palette = im.getpalette() or []
     if mode == "P":
         #
         # attempt to minimize storage requirements for palette images
@@ -1362,7 +1365,7 @@ def _save(
         else:
             # check palette contents
             if im.palette:
-                colors = max(min(len(im.palette.getdata()[1]) // 3, 256), 1)
+                colors = max(min(len(palette) // 3, 256), 1)
             else:
                 colors = 256
 
@@ -1435,7 +1438,7 @@ def _save(
 
     if im.mode == "P":
         palette_byte_number = colors * 3
-        palette_bytes = im.im.getpalette("RGB")[:palette_byte_number]
+        palette_bytes = bytes(palette[:palette_byte_number])
         while len(palette_bytes) < palette_byte_number:
             palette_bytes += b"\0"
         chunk(fp, b"PLTE", palette_bytes)

src/libImaging/Jpeg2KDecode.c

@@ -601,6 +601,7 @@ j2ku_sycca_rgba(
 static const struct j2k_decode_unpacker j2k_unpackers[] = {
     {IMAGING_MODE_L, OPJ_CLRSPC_GRAY, 1, 0, j2ku_gray_l},
     {IMAGING_MODE_P, OPJ_CLRSPC_SRGB, 1, 0, j2ku_gray_l},
+    {IMAGING_MODE_P, OPJ_CLRSPC_CMYK, 1, 0, j2ku_gray_l},
     {IMAGING_MODE_PA, OPJ_CLRSPC_SRGB, 2, 0, j2ku_graya_la},
     {IMAGING_MODE_I_16, OPJ_CLRSPC_GRAY, 1, 0, j2ku_gray_i},
     {IMAGING_MODE_I_16B, OPJ_CLRSPC_GRAY, 1, 0, j2ku_gray_i},

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},

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();
     }