Preserve hinted color spaces when deriving XObject image modes

pypdf/_xobj_image_helpers.py

@@ -367,16 +367,19 @@ def _apply_decode(
 def _get_mode_and_invert_color(
     x_object_obj: dict[str, Any], colors: int, color_space: Union[str, list[Any], Any]
 ) -> tuple[mode_str_type, bool]:
-    if (
-        IA.COLOR_SPACE in x_object_obj
-        and x_object_obj[IA.COLOR_SPACE] == ColorSpaces.DEVICE_RGB
-    ):
-        # https://pillow.readthedocs.io/en/stable/handbook/concepts.html#modes
-        mode: mode_str_type = "RGB"
+
+    preferred_mode: mode_str_type = ""
+    if IA.COLOR_SPACE in x_object_obj:
+        preferred_mode = {
+            ColorSpaces.DEVICE_RGB: "RGB",
+            ColorSpaces.DEVICE_GRAY: "L",
+            ColorSpaces.DEVICE_CMYK: "CMYK",
+        }.get(cast(str, x_object_obj[IA.COLOR_SPACE]), "")
+
     if x_object_obj.get("/BitsPerComponent", 8) < 8:
         mode, invert_color = _get_imagemode(
-            f"{x_object_obj.get('/BitsPerComponent', 8)}bit", 0, ""
-        )
+            f"{x_object_obj.get('/BitsPerComponent', 8)}bit", 0, preferred_mode
+            )
     else:
         mode, invert_color = _get_imagemode(
             color_space,
@@ -389,6 +392,9 @@ def _get_mode_and_invert_color(
                 )
             )
             else colors,
-            "",
+            preferred_mode,
         )
+    if mode == "" and preferred_mode:
+        mode = preferred_mode
+        invert_color = preferred_mode == "CMYK"
     return mode, invert_color

tests/test_xobject_image_helpers.py

@@ -5,10 +5,14 @@
 import pytest
 
 from pypdf import PdfReader
-from pypdf._xobj_image_helpers import _extended_image_frombytes, _handle_flate
+from pypdf._xobj_image_helpers import (
+    _extended_image_frombytes,
+    _get_mode_and_invert_color,
+    _handle_flate,
+)
 from pypdf.errors import EmptyImageDataError, PdfReadError
-from pypdf.generic import ArrayObject, DecodedStreamObject, NameObject, NumberObject
-
+from pypdf.generic import ArrayObject, DecodedStreamObject, NameObject, NullObject, NumberObject
+from pypdf.constants import ColorSpaces, ImageAttributes as IA
 from . import get_data_from_url
 
 TESTS_ROOT = Path(__file__).parent.resolve()
@@ -160,3 +164,31 @@ def test_get_mode_and_invert_color():
     page = reader.pages[12]
     for _name, image in page.images.items():  # noqa: PERF102
         image.image.load()
+def test_get_mode_and_invert_color_prefers_color_space_hint():
+    x_object = {IA.COLOR_SPACE: ColorSpaces.DEVICE_RGB, "/BitsPerComponent": 8}
+    mode, invert_color = _get_mode_and_invert_color(
+        x_object, colors=3, color_space=NullObject()
+    )
+
+    assert mode == "RGB"
+    assert invert_color is False
+
+
+def test_get_mode_and_invert_color_prefers_gray():
+    x_object = {IA.COLOR_SPACE: ColorSpaces.DEVICE_GRAY, "/BitsPerComponent": 8}
+    mode, invert_color = _get_mode_and_invert_color(
+        x_object, colors=1, color_space=NullObject()
+    )
+
+    assert mode == "L"
+    assert invert_color is False
+
+
+def test_get_mode_and_invert_color_prefers_cmyk_sets_invert_flag():
+    x_object = {IA.COLOR_SPACE: ColorSpaces.DEVICE_CMYK, "/BitsPerComponent": 8}
+    mode, invert_color = _get_mode_and_invert_color(
+        x_object, colors=4, color_space=NullObject()
+    )
+
+    assert mode == "CMYK"
+    assert invert_color is True